The MJ12 Chemical Insertion facility are a series of unmarked tunnels connected to an old water treatment facility, which was taken over by paramilitary troopers, later revealed to be MJ12 Troopers.
The facility is used for chlorine injection into the water, which is blamed as a chlorine spill and used as an excuse for water rationing.
Access to the main lab facility can be gained with the code 2167, which can be found at the top of a ladder at the entrance to the surface, or from a computer in the lab.
Helping Ford Schick to escape will result in lower prices to all goods Smuggler sells as a reward. In some modified versions of the game, Ford Schick will also offer the player an Augmentation upgrade canister as a reward in the final visit to Smuggler's Den. If the player manages to enter the sewer without talking to Smugger, Schick will have an unused conversation where he JC Denton doesn't know who he is.