tank the witness drain valves have a small reservoir that will retain a known volume of fluid as fluid passes from a leaking seal to the collector tank a small sample is captured in the witness drain valve once the witness drain valve reservoir is full the leaking fluid then flows on to a collector tank which is also provided during regular engine maintenance technicians push on a spring loaded drain valve located on the witness drain valve reservoir if fluid is detected the seal is beginning to leak and corrective maintenance may be scheduled while the leak rate is still within operational limits application_number US 97339401 A description referring to fig1 and 1 a there are shown perspective views of a drain system 10 in an engine compartment as conceived by the present invention the system includes multiple drain lines comprising upstream drain lines 20 and downstream drain lines 26 witness drain valves 15 are interposed between the upstream drain lines 20 downstream drain lines 26 the upstream drain line 20 is connected to the inlet end of the witness drain valve by means of conventional hydraulic interface connections such as threaded swaged or brazed similarly the outlet end of the witness drain valve is connected to the downstream drain line 26 the third leg of the witness drain valve 15 may be connected to a.