The Sewer

The Sewer is the third chapter of the first campaign, No Mercy.

The Survivors begin in a pawn shop which has been converted into a safe room. The usual tier 1 weapons are on a table inside, as well as four first-aid kits and an ammo stash.

This section of the campaign has the Survivors gaining access to an old warehouse and fighting their way through the sewers until eventually they arrive just outside the hospital.

Campaign
When starting from this chapter, the AI Survivors will grab:
 * Bill will grab a submachine gun
 * Francis will grab a submachine gun
 * Louis will grab a submachine gun
 * Zoey will grab a submachine gun

When the Tier 2 weapons are found, they will grab:
 * Bill will grab an assault rifle
 * Francis will grab an auto shotgun
 * Louis will grab an assault rifle
 * Zoey will grab a hunting rifle

Otherwise they will keep the weapons they had from the last chapter. (See The Subway for a list of weapons they will grab there).

If you're starting on this chapter, make sure everybody grabs a first aid kit and a weapon. They are entirely necessary to everyone's survival. If you started in an earlier chapter, heal up if you need to and take what you can. As there are lots of open areas on this level, the submachine gun may be a good option, though with luck Tier 2 weapons will become available shortly.

The first area of this map is very short if you know what you're doing. After opening the safe house door, immediately turn left and enter the door at the end of the alley. You'll find yourself in the back room of a diner. Remember to move quickly and keep an eye out for Special Infected. Smokers love to wait on top of one of the buildings, while Boomers get their kicks from either lurking around a corner, or dropping down from above.


 * If you choose to explore a bit, a loop is formed from the various alleys and rooms, eventually putting you back outside the safe room. While sometimes pills or grenades can be found here, it can be dangerous to go looking for them. If you get lost and circle this loop more than once, the AI Director will spawn a horde to attack you.

Once everyone is inside the diner, close the diner door behind you, slowing down pursuing Infected. Fight your way through the kitchen, and into the seating area. The entire front wall is made of glass, meaning that there is no choke point available. Once outside, be sure to stick together. The rooftops offer great vantage points for Smokers, and Hunters will prowl behind trucks or in dark corners, waiting to pounce on a lone Survivor.


 *  This is one of the four most likely times for a Tank to appear (especially in versus mode). If you hear one coming, be sure to stay in the open area right outside the diner. This offers the most maneuvering room, so the Survivors can employ anti-Tank strategies (see the Tank's page for more information). 

A gas station is all the way to the far right. If a gas pump is shot, the entire station will explode, killing any Infected underneath it. The rubble will also reveal a ramp up to a room which may have Tier 2 weapons, or other useful items. If nobody is near the station (which cannot be stressed enough), then blowing it to achieve these goodies may help your team to survive. (Blowing it up is not needed though as there is a ladder on the blue container that allows Survivors and Infected alike to access the room.)

To the left of the gas station is a lift, which is this campaign's second Crescendo Event. Once activated, it will noisily move the Survivors upwards to the rooftop of a nearby warehouse. (Not on the lift when it was activated? Fear not! There is a ladder on the side, allowing Survivors to ascend in such a situation.) Since the rooftops offer little protection from the Infected, and is vulnerable to a Smoker pulling off one of your buddies, a better place to hold off the horde is the back corner just behind the lift. If you have not yet done so, blowing up the gas station at this point will help you fend off the horde. The initial explosion will instantly kill any Infected nearby and also start a fire that will ignite any Infected that run through it.

Once on the rooftop, proceed along to the large-windowed room. If you are still fighting the horde when you get here, don't jump into the hole. Throw a molotov cocktail down into the hole to burn any incoming Infected and shoot any that try to come in through the window. Once the horde has been dealt with, you can drop down the hole into another room with a first-aid cabinet, an ammo supply, and sometimes Tier 2 weapons. When ready to proceed, either head down the stairs to the warehouse floor or into a room down the hall which has a view of the warehouse (and sometimes a pipe bomb).

''Note: Under the overhanging roof of the warehouse, in the back left corner, there is a metal door. This door can normally be opened by a button on the inside of the building, or by a Tank crashing through it. If the Tank breaks the door open before you start the Crescendo Event, feel free to punish him for his mistake. This door can also be broken by your melee shove, effectively allowing you to bypass the Crescendo Event. Hit the door roughly in the center until you hear the same sound that is played when you successfully melee shove an Infected. After hitting it for a while, it does break.''

Be sure to heal up before entering the warehouse, as this is a notorious ambush spot. Proceed quickly, and stay close together. Smokers frequently hide on the catwalks, while Hunters and Boomers will dwell among the dark aisles. Don't give them a chance to stop your advance. If they are encountered, punch a Smoker's victim to release them from its hold, and destroy Hunters as quickly as possible. In the event of Boomer vomit, quickly move to a nearby wall, and move as soon as you can see again.


 *  This also happens to be the second of the four likely spots for a Tank to appear. If he appears, don't wander too far from the first part of the room, since the Smokers, Hunters, and Boomers are just itching to add to the chaos. Instead, prepare for this battle by hitting the button to open the door before entering. If a Tank appears, retreat back outside, where it may be more easily disposed of. 

Once out of the warehouse, move down the alley and follow the hallway until you get to a stairwell. At the bottom lies a generator room, with a manhole at the other end. Since the generators provide lots of cover for Special Infected, make sure to check behind these as you go. You have two options to get to the sewers.


 * 1) Get to the manhole on the other side of the room, and drop down onto a wooden plank above the sewers.
 * 2) In the middle of the right wall, there is an often-overlooked room. This room contains another manhole into the sewers, and sometimes a pipe bomb or a molotov. However, Special Infected are able to crawl out of this particular manhole, so watch for that.


 *  The generator room is the third location a Tank will often appear. If you have not encountered one yet, you will here. Either immediately leave the confined spaces of the stairwell, or retreat back the way you came while shooting. Molotovs are dangerous in the limited spaces this area contains. 

If you dropped onto the plank, there will be a "T" intersection. Take the right-hand turn, and then make a left. If you took the other route, proceed forward to an intersection, and then continue forward. This will place both groups traveling along the same path.

While the sewers themselves are rather wide-open, there are many small passages off of them. Special Infected love ambushing unsuspecting Survivors out of them. Avoid this by keeping your distance from them, and staying close together. The path to take is lit up by overhead lights, so stay out of the dark areas to proceed. Eventually, an open door will appear along one of the walls. Pass through it into the room beyond (closing the door behind you as always). There will be an ammo supply on the ground, and there is a chance that grenades, pain pills, or even a health pack will be here. Enter the nearby tunnel to proceed.

After the tunnel turns right, move forward until it opens back up into the sewers. There is an offshoot to the left where Special Infected will hide, so be wary of that when you pass it. Once out of the tunnel, follow the same lighting rule to get to a ladder. This ladder will take you out of the sewers. Since Special Infected love any areas Survivors must climb out of, so it is almost guaranteed that one or two are waiting at the top. If someone has a molotov, they should carefully throw it so that it lands just outside the sewer exit, burning the would-be ambushers. Failing that, make sure the team leaves in shifts of two so there will be someone to help out. If all four of the Survivors leave the sewer at the same time, a Boomer can puke on everyone at once, which makes this bad situation even worse.


 *  This stretch of the sewer is the last of the common areas a Tank will spawn. Move to an intersection where there is slightly more room to move. If in the second area, do not face him on the street. Cars litter the road, and are a sure-fire way of someone getting incapacitated or killed. He will follow you into the sewers, so take him there rather than put everyone at risk up above. 

Everyone out? Good! The hospital is in sight. While it may be tempting to bolt straight to the safe house, many teams have died by doing that. Smokers will dwell above the entrance, while Hunters and Boomers will attempt one last attack inside. Use the ambulance just outside the doors as a waypoint, and quickly check inside it. A healing item will often spawn in here, which will be valuable when you proceed. If you are playing in versus, the item won't be valuable, but a Special Infected may choose to hide in there. Either way, swiftly enter the hospital, and move behind the counter to enter the safe room. Stop only if you must shoot a Hunter off a teammate.

Survivors
Remember all those devious places the Special Infected like to lurk? The human-controlled Infected will ruthlessly use these to slaughter your entire team. The best way to counter them is to deny them a good chance to do so. Grab your weapons quickly, as well as the second pistol which now presents itself, and rush to that diner. The less time you spend here the better.

If you're feeling lucky, go through the doorway to your right. This will lead you through a storage area, and on the other side is a small garage area. This area may hold Tier 2 weapons, and it's possible that other useful items (such as pills and various grenades) will spawn in the storage area. If you do do this, move fast. The longer you're out here, the longer the Infected have to mess with you. As long as everyone moves with a buddy, everything should be fine. Once you've gotten your fill, run down the alley, turn left, and go inside of the restaurant.

Stick together! Yes, yes, you already know, but don't even split up into two groups of two. The large amount of hiding areas makes this a dangerous level to get separated in.

Always blow the gas station in order to search the adjacent room. You don't have the advantage of keeping Tier 2 weapons from the last section.

Be especially careful of shooting when you see a Special Infected and hear a Witch; they like to conceal the Witch from your initial line of sight, and you probably know very well what happens when you shoot at the Witch.

Once you're in the room with the hole—assuming you took that route—hurry up and drop down. If a Smoker drags somebody out from the window, it's almost certainly a kill. After entering the room below, which has ammo and a First-Aid Station, be sure to stay away from the windows. They can still pull you out, and needless to say, that's not much fun, either.

Have the last person run backwards down the dark hallway after the warehouse. This way, he can protect himself from any Infected planning a flanking maneuver

Always enter the room on the right wall of the generator room. It is much easier to protect against lurking Special Infected in there. Once you've entered the Sewers, be especially wary of the tunnels. They're a great place for Infected to hide in, and getting ambushed due to one's carelessness when running by the tunnels isn't very nice. Make your way to the last manhole of the sewers. When there, try your hardest not to let anyone go up alone: this is a crucial choking point for the Infected, and they can pull you away or pin you down one by one as you get off the ladder. Get everyone up, one way or another, and make a run for the hospital.

The Infected
Techniques:
 * Pre-Diner ambush - The Smoker waits on the rooftops, the Boomer in the alley to the left of the diner, and the Hunters in the alley to the right. As soon as they come in sight, the Boomer vomits over as many as possible. Immediately afterwards, the Smoker and the Hunters grab three of the Survivors, being sure to get any not covered with bile. If done right, this can be a game-changing maneuver, or even outright kill the entire team with some luck.


 * Three-Survivor pin - Obviously, it is possible for three Survivors to be incapacitated at once by using the Smoker and two Hunters. Because the Tank frequently spawns early in the level, it is possible for him to concentrate on one Survivor enough to kill it, though it is risky. To help with this, the Boomer should also target this Survivor, vomiting and then clawing it. Once they are down a member, set up an ambush somewhere dark, such as the warehouse, and grab all three of them. They won't be able to retaliate if done quickly.


 * Witch Ambush - Though this is a very recognized technique, the Sewer is arguably the best stage for this trick if a Witch spawns in the depths of the sewer. The dark lighting allows a Special Infected to block out the Witches glowing red outline by crouching in front of her. The darkness can also block out the Special Infected themselves, especially if they are a Hunter. When a Survivor sees you, they'll shoot you, and alert the Witch. When another Survivor comes to help the incapacitated, you can pounce or rope them. A Boomer will have already exploded, and hopefully splashed onto the Survivor, pretty much dooming them, and earning you points. When performing this trick, it's good to have another special Infected, preferably a Smoker, to grab a third Survivor.

Boomers: There is plenty of opportunity to wreak havoc among this level. Try dropping off a roof into the middle of the Survivors for a surprise, or vomit down upon them, letting gravity extend your reach. Hide in areas they will have to pass through to make the arrival of a horde inevitable. Stay out of any open areas where you will be vulnerable, and spawn in an area in front of the Hunters. Whenever a Tank is attacking, take advantage of the situation and catch as many Survivors as possible in your bile.

Hunters: This map is more difficult for you than for the other Special Infected. Team up with another Hunter to maximize your effectiveness. Climb to a high place before pouncing in order to increase the bonus damage you do, such as the roof opposite the diner. When the Survivors activate the lift, wait at the top, and then pounce on one. Because the Hunter pushes back his victim, you are likely to knock the Survivor off the lift, giving you a bit more time while his buddies figure out where he went. When the Tank appears, jump on healthy Survivors he is going after. Even if you die, you allow the Tank to catch up and tear that Survivor apart.

Smokers: This area is made for you. At the beginning, climb to the top of the rooftops as quickly as possible. If you climb above the Safe House, you have a good line of sight to yank a Survivor out of the diner. If possible, always try to be behind the Survivors, since pulling someone backwards in the level is more effective than pulling someone forwards. Pulling a Survivor back down the hall after the warehouse is a particularly good example. If you can manage it, try to strangle a Survivor who just went down the manhole. At the hospital, either grab the last Survivor to climb the ladder, pulling them back down into the sewers, or the last one into the hospital. When the Tank is around, be sure to target healthy Survivors the Tank is not currently chasing. Also, you can get onto the fire escape near the climbable building by the safe room; people do not expect you to be up there. If the Survivors don't shoot the gas station at once, another risky strategy would be to hide behind one of the gas pumps in the gas station. Once the Survivor move close enough, grab one of them. If they shoot you, there's a chance they'll shoot the gas pump and kill you in the explosion, along with your victim. If you're lucky, this could even result to death of all the Survivors if they are close enough.

Tanks: First off, be sure not to break down the metal door, or you will allow the Survivors to skip the Crescendo Event. When playing as the Tank, be careful to avoid fire, this will cause your health to go down significantly until you die. Go after the weak Survivors first, pummeling them until they can't get up. Since the Survivors are likely to be faster than you, you need a way to catch them. If you ignore the first downed Survivor for a few seconds, somebody will inevitably try to get them up, during which time they can't move. Use that time to run up and put them in the first chum's shoes.

Survival
Rooftop Corner Method


 * Once the lift has risen, you'll be facing a rooftop. In front of you is the corner where this roof meets with the wall. This corner is an effective position to fend off the Infected. Two people cover the lift's stairs, whilst the others cover the further rooftop. The Common Infected will mostly charge in thin lines. This method deals with Boomers, Smokers, Hunters and Tanks effectively. However, it will only work effectively, if all of the Survivors are bunched into the corner tightly.


 * The Boomer is dealt with due to the fact that if you are all standing close enough to the corner, he will spawn on the rooftop of the building ahead of you. After which he will jump off and hit the ground. As he does, he will explode, removing him as a problem. If one or more Survivors leave the corner, the Boomer may spawn below you and ascend the ladder, or spawn above you and drop down. Either way normally results in most of the Survivors getting covered in bile.


 * Hunters are forced to ascend the ladder, as they believe that there is no other good location to pounce you from. This gives the Survivors ample time to kill him as not only does it take a few seconds for him to come off the ladder at the top, but he hesitates to pounce once he's up. Hunters rarely attack from across the rooftop. Even if they do, the two covering the rooftop should be able to defeat him before he can attack.


 * Smokers will not drag anyone off the roof if the players are close enough to the corner. Instead, they will appear on the roof above you and drag people against it. At most, this will take people a few meters away and then they can easily be freed by hitting them. Smokers may also fall for the same ladder tactic that the Hunter does, but this is rare.


 * With your elevation and lack of obstructions, you can spot the Tank long before he can get you. This gives the team a lot of time to defeat the Tank before he can reach the Survivors, effectively removing him as a problem. Generally, the Tank will climb on top of a truck and then onto the roof, giving him a final run to get to you, where your team can finish him. However, he may occasionally climb the ladder which will force the team to fall back and head over to the other side of the rooftop.

Second Floor Method


 * The first room on the second floor that you enter via the windows on the rooftop is a fairly easy position to defend. This is a popular and effective place to defend mostly because in this room, there are a total of five pipe bombs and three Molotovs. From the back of the room, there is a corridor-like passage. Facing away from Mercy Hospital, two Survivors can shoot down this passage and restrict movement of the oncoming hordes. The other two can face towards the other direction that the Infected can attack from and defend there. If things get too much to handle at the front, one of the Survivors guarding the second passage can move over to help defend the first one.


 * This tactic deals well with Smokers, as it is too close for them to be effective. It also deals well with Hunters, as they are heard long before they are seen and infrequently, they don't even reach your position. The downside to this tactic is the Boomer. However, as long as the team stays fairly far back and shoots him before he can do anything, they shouldn't have a problem. The Tank is dealt with by either fighting him whilst maneuvering around and around the passages, or by using one of the three Molotovs to set him alight and then avoid him until he dies.

Behind the Scenes
In earlier footage, it seems that the players had to get to the roof by going through the building to the left of the gas station, not by using a lift.

An early picture of the front of the Hospital shows that there was to an advertising billboard to the left of the hospital at one time.

Trivia

 * The gas station explosion instantly kills anything standing in the center of the station, including Tanks and Witches. Experienced players (with good timing) can attempt to lead a Tank under the station and blow it up at the right moment, causing an instant-kill and skipping the entire battle.
 * The Sewers is one of the most modified maps in the history of Left 4 Dead. Several older versions had players go from warehouse to warehouse, through a gas station market, and even up a truck to get into the main sewer entrance.
 * If you look closely when you get to the warehouse, you can see the helicopter land on the roof of the hospital, (and if you're patient enough, it going back and repeating) possibly hinting there were other Survivors that were in the city and contacted the pilot. It may also explain the pilot's "incident" in the rooftop standoff.
 * As a Smoker in versus, it is possible to kill or incapacitate a Survivor by pulling them off the roof (the one you reached on the lift). This either done by being on the ground or on top of the warehouse.
 * Ironically, the sound of the gas station detonating into a violent explosion does not attract any Infected, while the small sound emitted by the lift does.
 * It used to be possible for the Survivors to break down the metal door to the warehouse and bypass the second Crescendo Event. Although this is not a bug, it is most likely a placement mistake on Valve's part. An attempt was made to fix this door, but it was only half successful. About 50% of the time, the door can still be broken with enough hitting. Of course, it takes a long time to break the door with melee, and with the uncertainty as to whether or not the door might be breakable for you, your team will have either wasted too much time hitting and realize that this time around it is solid, or they'll get tired quickly even if the door is breakable. Either way, it's rarely ever attempted in versus, and still often skipped in campaign.
 * The restaurant that the Survivors go through at the beginning of the chapter is called "Burger Tank". This is a reference to Burger King, and possibly the Tank.
 * In the sewers, in the room with the small tunnel you have to go through, a Hunter (with difficulty) can get the floodlight into the tunnel, blocking the survivors’ path. If it’s in feet first, it’s possible for the survivors to bypass it. Otherwise, they'd have to melee it around the corner to take the alternate way out. (Most people give up on the corner)
 * The convenience store at the gas station is named, Pump 'N' Run, which is a reference to the game's shooting and running style of gameplay.
 * Standing near the gas station when it explodes and surviving (right after spawning in Survival Round) will make the Survivor temporarily deaf.