OK, let's recap.
We have a Sink and Outside Shower plumbing
configuration.
The Adle is correctly in By-Pass mode.
When City Water is connected, everything works
correctly . . . hot & cold water have pressure and flow.
When City Water is not connected and the Pump
is used, pressure/flow stop as soon as city water built up pressure
is released/used.
So something is wrong with the Pump or Pump
water lines.

[] fresh water tank vent could be blocked - - -
low likelihood
[] fresh water feed line could be blocked - - -
can you blow air into the hose (hose that connects to Pump filter) and
hear bubbles in the tank?
[] Are all pump fitting air tight? No leaks.
[] If sure pump feed line is clear and no air leaks, time to
remove the pump.
Consider Taking Pump apart**, confirm there is no
junk in the passages, put back together and try pumping again.

Yes, and probably ly the cheapest to replace if you made a mistake!ChanW said:True! I've considered that too.
The strange 'extra AC vent' would be a perfect entry point, with a near direct access to the hollow shower wall that leads down to the electrical distribution area in the bench seat.Sharon_is_SAM said:@ChanW, why not use the roof vent as the access point for the solar mod?