[A/S] 1965 Overlander Plumbing question

[SHMossLanding@xxxxxxx]

When hooking up to city water, my lines go from the hose inlet, to a check 
valve then through a regulator(set at 60PSI) then into the system.  There is 
a pipe that feeds off the main line, between the regulator and the toilet 
pipe.  this pipe leads to a drain pipe, inline with the hot and cold drains 
at the rear of the coach. Does any know what this pipe is for.  When on city 
water it runs a little bit all the time.  Less when the pressure was reduced 
to 60PSI.  Any ideas?  Any help would be appreciated.

                                                       Chuck & Lynn
                                                       1965 Overlander