Abstract: An improved drain mast assembly for a gas turbine engine is connected to an outer surface of a nacelle of the engine and has a plurality of liquid drain lines terminating within the assembly. The assembly comprises a plurality of liquid collection chambers installed within the drain mast assembly with each of the chambers coupled in liquid receiving relationship with a respective one of the liquid drain lines. Each of the chambers collect drain liquid from a respective one of the drain lines. A valve extends from each chamber for selectively draining the collected liquid from each of the chambers for identifying drain lines having relatively high drain-rates. Each of the chambers is separately removable from the drain mast assembly in one form or all chambers may be simultaneously removed in another form of the invention. Each chamber further includes a transparent view window for visually determining a volume of liquid collected by the chamber.