Taken from Submarine Trim and Drain Systems, Navpers 16166, Chapter 3A...
"The drain pump, located in the pump room, provides suction for the drain system. The pump is started and stopped by means of an electric push-button switch located nearby in the pump room. The drain pump has a suction and a discharge connection. A suction line equipped with a strainer and a sight glass connects the suction side of the pump with the main forward and after drain lines, usually called the drain line forward and the drain line aft. The drain line forward and the drain line aft can be cut off by shutting their respective stop valves, located in the pump room. "
"...the drain line forward extends to the forward torpedo room and provides pumping connections for the two bilges and the pitometer log well in the after section of the torpedo room. The drain line terminates at the forward bilge manifold, with two valves controlling the suction from the poppet valve drain tank and the forward bilge."
"There are no drain line connections in the forward battery compartment. "
"The drain line aft extends to the after torpedo room and contains pumping connections to the sumps in the compartments in the after section of the submarine. There are no drain line connections in the after battery compartment. The forward engine room has two bilge sumps connecting with the drain line aft through two individual lines. The after engine room also has two bilge sumps which connect to the drain line by means of two separate lines. In addition to the bilge sump pumping connections, the drain line aft contains also a suction line to the collecting tank, making it possible for water from the collecting tank to be pumped out through the drain system.
There is one bilge sump in the motor room.
The drain line aft terminates in the after bilge manifold in the after torpedo room. Here too, the manifold contains two valves, controlling suction from the forward and after bilge sumps."
"Returning now to the pump room, the drain pump suction line carries a branch connection to the pump room bilge manifold. This manifold contains three valves controlling suction from the three pump room bilge sumps.
The drain water from the gun access trunk, the cable trunk, the periscopes, and the antenna wells empties into the pump room bilge and collects in the sumps from which it is pumped when required.
The drain pump has three points to which it may discharge: 1) the overboard discharge; 2) the compensating water main; and 3) the trim system. In addition, the drain pump is so interconnected with the trim manifold that it can discharge water into the trim system instead of into its own piping."
"Every branch suction line to the bilge sumps has its own bilge stop valve. When it is desired to pump out certain bilge sumps, or wells, the valves leading from them to the drain line and the pump are opened. The required discharge valves are then opened to the overboard discharge, the compensating water main, or the trim system, depending
upon the conditions. Then the drain pump is started and the pumping begins. When the pumping is completed, the pump is stopped, and the valves to the various lines used in the operation are shut. "
"Bilge water should not be discharged directly overboard if there is danger of detection by the enemy, because the oil in it will rise to the surface, indicating the presence of the submarine. Instead, bilge water should be pumped into the expansion tank, where the water separates from the oil before being discharged overboard.
If the trim system is used to receive the bilge drainage, it is possible to pump this water into the variable ballast tanks. But this may be a hazard to security, because discharging variable tanks to sea during trimming operations will allow bilge oil to rise to the surface, leaving the telltale oil slick."
If you want more operating details, I can post the step by step process.
