I'd connect to city water, run water through all the systems to purge air. disconnect city water. make sure you have water in fresh tank above the pick up tube.
and then see what the result is.
the pump should resist back flow- even if turned off and the tap is open- it shouldn't "suck" air
my own pump was having some issues with priming and I found deposits of minerals on the diaphragm. easily cleaned out and reinstalled
( I have now a spare new pump on my shelf...I ordered it in a panic before I could get to and service my old pump).
I need to get better about prepping for a trip a week before departure rather than a couple of days before, so as to have time for these little things
2006 Pleasure Way Lexor TD on a Chev 3500
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