"Peggie Hall" wrote


A failing/failed diaphragm wouldn't cause the pump to leak...it
creates an air leak in the pump ....

Ah, light dawns! It's harder to make things vacuum tight than pressure
tight and much, much, harder than watertight. Developing porosity in
the rubber would do exactly what you describe.

The sink drain "T" into the head intake line works great although
it means a lot of head pumping.

Most likely because the toilet is pulling air through the sink
that's preventing from priming. Put a plug in the sink when flushing
with sea water...when flushing with water from the sink, the sink
needs to be at least half full. Just running water down the sink
drain won't work 'cuz the toilet will pull more air than water.

No, it works perfectly in normal head mode. There is a valve in the
line from the sink to the head intake line.

What I meant by lots of head pumping was filling a 13 gallon holding
tank by pumping the head. I really shouldn't have posted that point
because it only applies to our very funky marina where there is no
water hose bib within reach of the pump out station. I tried filling
the holding tank by pumping fresh water through the system to avoid
motoring back to the dock to fill with the hose through the deck pump
out the way any normal person would. Now that I've done that once,
motoring back and redocking doesn't seem like as much work as it did
before

--

Roger Long