The injector steam also pre-heats the water entering the boiler, improving boiler efficiency. Excess spilled down the overflow pipe located behind the trailing truck. Often, exhaust steam from the valves was piped to the injector, however, builders also used fresh steam from the boiler. The delivery pipe ran diagonally up the fireman's side of the locomotive from the tender hose, under the outside end of the grate, and was often concealed by boiler lagging.