would adding one check valve to the bottom of the water tank where the weep comes out solve the problem?
Check valves have no "charge." Do you have hot water in your tank? Do you have hot water on soap and cold on rinse? Use the method I described above except run each bay on soap, allow the plumbing to the pump to get hot, then switch it to rinse. If there's a bad check valve the line back to the tank will get cold.