Okay, been thinking more about this. Your return line must be plumbed right behind the pump on the suction side. So when you are trying to prime the pump with the miser valve in the wrong position, the pump is drawing in air from the shower Miser return line instead of pulling only from the fresh tank?
My miser return line is plumbed to the top of the fresh tank, so for us, it doesn't matter what position the miser valve is in until we open the shower valves. The pump always draws only from the tank, instead of the return line and the tank.
Make any sense? Maybe I answered my own question
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Scott and Liz - Southern NM
2012 Wildcat Sterling 32RL - w/level up (best option ever)
2007 Chevy 2500HD Duramax
Reese Fifth Airborne Sidewinder