County Sewer Mainline

 is a sewage tunnel which can be accessed from either inside the Sewer Waystation or a sewage grate along the Potomac, just north of a raider camp under the west point of the Arlington Memorial Bridge. It goes under Grayditch and Arlington Cemetery, but has no access point there.

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 Home
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 a Tales of a Junktown Jerky Vendor, and 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).

Gallo's Storage Closet
Gallo's storage closet can be accessed using Gallo's Storage Key, or by picking its lock.

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, ammo 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 the original Fallouts.

Notable loot

 * Nuka-Cola Quantum in a safe
 * 2 Pre-War Books with Gallo's Nuka-cola collection
 * A Stealth Boy hidden in a box
 * 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 can be retrieved from Gallo's corpse

Appearances
The County Sewer Mainline only appears in Fallout 3.

Bugs

 * If the player jumps onto the freezer unit where Gallo keeps the feral ghoul corpse, they can get stuck. This requires a reload from an earlier save to fix.
 * 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".
 * After exiting through the grating to the Potomac, the area may refuse to load, locking up if you try to return back through the grating, and the sewers will become inaccessible from the other end as well.

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