Water pump running non-stop/water system problem

If you have a tube and valve before the water pump to suck up anti freeze to winterize, try putting the tube into a bucket and see if the water pump sucks up the water.

Some rigs have a valve that must be turned either one way for hose connection to the outside so water does not fill the tank, or the other way to build up pressure just using the pump from the tank. Pump use without that valve just causes water to recirculate.