Originally Posted by Filthy-Beast
or the hoses are reversed and it's trying to push into the tank.
I would think not, because he states that everything works OK when hooked up to city water.
The image above shows that if the pump is running backwards, it is trying to draw water from the system and pump it into the FW tank. There could be some water dripping from a faucet or two when this happens, due to pressure differences in each circuit. And the pump is trying to pressurize the FW tank, which is causing water to dribble out the overflow tubes. There is probably air escaping through the vent line to the tank fill tube, as well. If that is happening, then this is definitely the problem.
Check for air escaping from the vent line. OR, try reversing the electrical leads on the pump to see if that solves the problem.
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