Gabe, your solution suggests you have a problem. The tank should fill without removing pressure by pumping water out of the tank. Look at the overflow, it is probably plugged, as water comes into the tank air should be vented via the overflow (not the dump). At least on our water tank there are 2 pipes on the front, 1 at the top, the over flow, and 1 at the bottom, the drain (water to the pump comes out of the tank at the rear, bottom). IIRC, the overflow is a 3/4" pipe, the drain is a 1 1/2 pipe, both go through the floor and drain outside. Some folks had problems with the tank draining out the overflow while they were driving and might have fixed it with a valve, not a good idea, overfilling the tank will stress the walls and seams and could lead to failure. The same goes for relieving the over pressure via the pump and water, once the tank is full you need air flowing to equalize pressure, otherwise you create a vacuum in the tank that can also stress and damage it. Be sure you have free air flow to the tank BOTH ways, filling and using the water!
Dave, Bobbi and Fenway
2005 38' FDTS Alpine Limited, 2016 Jeep Grand Cherokee Limited
Cape Cod, MA