County sewer mainline

The county sewer mainline is a sewage tunnel which can be accessed from either inside the sewer waystation or a sewage grate along the Potomac River, just north of a raider camp under the west point of the Arlington Memorial bridge.

Background
Although it cannot be accessed through these locales, this network of pipes goes under Grayditch and Arlington Cemetery, and serves as a thoroughfare for wastelanders heading to and from Washington, D.C. It is the home of Gallo, as well a number of feral ghouls and radroaches, and contains a large number of workbench items.

Gallo's hideaway
Nearby the waystation access point (the right path after entering via the waystation) can be found a hostile ghoul named Gallo, whose room is located past several traps in the northwest region of the sewers. On Gallo's person can be found Gallo's storage key which is used to access a storage closet nearby. Gallo's room also contains a small Nuka-Cola collection, a safe, as well as a pen of radroaches. There is a bed here too, and quite a few shelves. If Gallo is killed, you can use his home as your own (though you cannot technically own it).

Sewer management main room
The sewer management main room is located in the central region of the mainline. It is occupied by a number of radroaches and feral ghouls.

Sewer management storage
The sewer management storage closet can be accessed from a terminal behind a locked gate nearby. A number of chems, ammunition and workbench items can be found.

Sewage tunnels
The sewage tunnels that compose most of the mainline are littered with the remains of dead mercenaries and wastelanders. These are often marked by the presence of feral ghouls. Boxes of ammunition can be found near many of the remains.

Also in the tunnel between the sewer management main room and Gallo, there's a strange skull with glowing eyes stuck on a metal rod, with two smaller rods crossed just under it. It could be a reference to the Khan raider clan from Fallout 1 and 2.

Notable loot

 * Nuka-Cola Quantum in a safe.
 * 2 pre-War books with Gallo's Nuka-Cola collection.
 * A Stealth Boy hidden under a box in Gallo's storage closet.
 * Big Book of Science next to the terminal used to access the sewer management main room.
 * 2 pre-War books also near the terminal.
 * A copy of Tales of a Junktown Jerky Vendor, carried by Gallo.
 * 2 smaller than normal Nuka-Cola trucks as seen in the photo of Gallo.
 * A random loot safe near the Capital Wasteland exit that's embedded in the ground, by some shelves.

Appearances
The county sewer mainline only appears in Fallout 3.

Bugs

 * In a small room with a staircase near the exit to the Capital Wasteland, the player might find themselves swimming down the staircase rather than walking, having an oxygen meter displayed and the ability to "drown".