yeah, its loosing pressure, somewhere...very slowly. check the city hookup. does it drip.....drip.....drip....? there's a check valve in there somewhere that keeps the pump from just sending the contents of your fresh water tank right out the back. could also be internal to the pump.
mine cycles alot more often than that. (because my check valve is shot). Even when I have the plug in the city hookup. unless you teflon-tape the threads and knuckle it down, it isn't really sealed up perfectly, so there's always a little leakage. earlier this season, I found that my fairly new plug had a pin hole in it. guess how?
the stream was so thin, it was only detectable when I was standing in it. I thought some ill-mannered canine was marking his territory, for a split second.
I'd like to replace the check valve...even bought a replacement...but its unreachable.
the bathroom will need to be removed in order to get at the damn thing.