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.

Strategy
Also see: Tactics

All campaign walkthroughs are done on Normal difficulty in single player, and are meant to give tips on what to do and generally point out things that might otherwise be missed.

There are, of course, a few key things to always remember:
 * Stop, look, and listen.
 * Stopping to observe your surroundings might allow you to prepare for something nasty, like a Witch, Tank, or special Infected in a really bad place for them to be.
 * Things can always get worse.
 * Are you and your teammates all hurting, your health down under 50%? Well, guess what? The Director doesn't care. You are now facing a Tank with Tier 1 weapons.
 * Teamwork.
 * This cannot be stressed enough. Left 4 Dead is supposed to be a cooperative game. Communicate with your teammates, if you're playing with others, or if you're by yourself with the AI, point out things they might otherwise miss. In all cases, watch out for each other and take care of each other. You are not going to survive the zombie apocalypse by yourself.
 * Be ready for anything.
 * Don't panic.

Infected prowl through the buildings, and there are many places for Special Infected to lurk, so always keep your wits about you. Witches are all but guaranteed to spawn here, though can usually be avoided as long as you spot them first. Tanks will frequently appear in open areas, but don't count on it.

Campaign
At the beginning...
 * 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...
 * Bill will grab an Assault rifle
 * Francis will grab an Auto shotgun
 * Louis will grab an Assault rifle
 * Zoey will grab a Hunting rifle

Note: These are what the Survivor AI will usually grab.

Otherwise they will keep the weapons they had when they entered the safe room.

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.

Once everyone is inside, close the door of the diner 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 secondary weapons, or other useful items. If nobody is nearby the station (which cannot be stressed enough), then blowing it to achieve these goodies may help your team to survive.

To the left of the gas station is a lift, which is this campaign's second crescendo event. Once activated, it will noisely 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. Once on the rooftop, proceed along to the large-windowed room, and 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 grenade).

''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. It is also possible to open this door through many repeated melee attacks, and puts the survivors at the bottom of the stairs. If this route is taken, it lets the survivors skip the Crescendo event entirely. As always, tactics such as this are not recommended, as they take away from the gameplay, and are considered unfair during versus gameplay. However, if the Tank breaks the door open, feel free to punish him for his mistake.''

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 following 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 grenade. 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, 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, 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 entire team leaves at around the same time to ensure there will be someone to help out. (Warning! Do not leave at exactly the same time, or else a lurking Boomer will make you wish you hadnt)


 *  These sewers are 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, be sure to take him out before leaving the sewers. The Tank can climb the ladder after you, and while the open area might help, the fresh Infected and other nasty surprises will ensure your quick demise. 

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. Move towards 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 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.

Stick together! Yes, yes, you already know, but don't even split up into two groups of two. The large amount of hiding areas make 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 careful of shooting when you see a Special Infected, they like to make you shoot at them when they are near the witch.

After dropping down the hole into the room with the ammo and health-cabinet, be sure to stay away from the windows. Getting yanked out by a Smoker is never fun.

Have the last person run backwards down the dark hallway after the warehouse. This way, he can protect himself from any Smokers who try to grab him.

Always enter the room on the right wall of the generator room. It is much easier to protect against lurking Special Infected in there.

The Infected
See also: The Boomer, The Hunter, The Smoker, The Tank

Over-all Tips:
 * Lone wolves. Mmm, mmm, mmm, tasty.
 * The Survivors all have outlines around them. Green means they're healthy. Yellow means they're hurt. Red means they're low on health. You can probably discern which to seek out first.
 * Think like a Survivor. When you play as one, when are the worst times that something could come at you? Exploit that knowledge.
 * Teamwork, as aforementioned. Has a Boomer gotten their bile all over the Survivors? Jump one of them or a clean one. They can't see their teammates' aura until they're clean... and by then it might be too late.
 * As much as teamwork is a strength for you and your enemies, a lack there of will be their downfall. If you can focus all of your energy on killing one of the Survivors, the rest will be that much easier to take down. Not only will they have one less gun, but they will have three Survivors to your four incapacitating 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. Right afterward, the Hunters and Smoker 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.


 * Cheap door ambush - If the Survivors are attempting to break the door in order to skip the lift, then this strategy may work. The Smoker should wait at the top of the stairs, the Hunters on the stairs crouched, and the Boomer at the bottom. Be ready at all times. The moment the door breaks, the Boomer should vomit its bile. In the confusion, the Smoker and Hunters grab the survivors, starting with any not covered in the bile. Like the other ambush, this can be a game-changing technique, and will give the cheaters what they have coming. If the two ambushes are coupled together, it is likely to win the game right there. Just be sure to play the survivors first if you also plan to break the door! No need to give the other team a chance to follow your lead!


 * 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 them selves, 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. When the survivors activate the lift, wait at the top, 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.

Smoker: 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.

Tank: 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 molotovs, since you will die within 40 seconds of being lit on fire. 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.

Trivia

 * 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 enterance.
 * If you look closely when you get to the warehouse, you can see the helicopter land on the roof of the hospital,(and if your 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.
 * This map has a terrible blocking point. A dumpster at the top of the ladder, to exit sewers, can be moved in front of the ladder blocking the exit. This is can not be moved with out help of an infected.
 * The metal door at the other end of the loading bay from the lift can be broken open by the survivors using thier melee attack. Infected can't move through the door in ghost mode.
 * Inside the wharehouse after the lift crescendo event, a hunter or smoker can block the exit doorway with a forklift.