A single hole in the hull, one-foot square and 15 feet below the water line admitted water at a rate of 13,900 gpm. Efficiently operated drainage systems could remove water and keep engineering spaces operating that otherwise might have to be abandoned due to holes, cracks in the hull and progressive flooding.

On large ships, the main drainage system was a loop system serviced by up to nine centrifugal pumps operating through eductors at 1,200 gpm each and five steam-driven reciprocating pumps at 225 gpm each, all installed to take suction from the main drainage system with a total capacity of 12,000 gpm.

On small ships, the main drainage system was a single 2 ½-inch pipe. It ran fore and aft, usually amidships, and was serviced by up to four 200-gpm fire and bilge pumps, one in each boiler and engine room. Reach rod valve assemblies were installed and were generally operated from the DC deck.

On carriers, battleships and heavy and light cruisers, the main cut-out valves in the system were operated from control stations, generally on the DC deck.

There were also many check valves and stop-lift check valves in the systems; they were operated from distant control stations as well.

On some ships towards the end of the war, the main drainage system was used to drain “floodable” voids used in counter-flooding after such voids had been flooded, and to empty fuel oil tanks that had been ballasted down with sea water.