Originally Posted by alpinedrvr
Yes ,yes,yes, Dave I had not thought of that at all. I kept thinking of the city water pressure as I was filling and not the air needed as the water pump is pumping out of the tank. Hmmmmmm I'll do some more thinking (which is dangerous!)
Can you explain the reason for the CV and where/why you added it?
My coach has the same siphon problem and lost water out the overflow when stopping.
I added a 1/4 vent line with a check valve, (like this http: //www.usplastic.com/catalog/item.aspx?sku=57176&gclid=CMXcl7b89LUCFe4-MgoduVUAsg), which prevents water from flowing out but allows makeup air in when pumping water out.
To prevent pressurizing/damaging the tank when filling I added a ball valve in the 1/2" overflow pipe.
However I MUST remember to open the ball valve when filling.
BTW, IMO the best solution would be an overflow/vent hose that terminates 2 or 3' higher than the top of the tank, (no check or ball valve needed), but I can't find a good way/path to run one in my coach.