I am in the middle of installing a drainback system with evacuated tubes and two pumps. I have a 1/4"+ per foot slope on the panels and much greater slope everywhere else. The system won't consistently drainback fully. There is probably a 1/4 of the water in the system still in the pipes when the pump turns off. I've added a loop from the top of the drainback tank to a couple of feet above the supply side and that helped but it is inconsistent. Would making that loop higher be the answer or a vacuum breaker up high with a air vent on the drainback tank? Any ideas? Thanks in advance. Dean

I moved my heat exchanger to the supply side of the tank and that fixed everything. System works great now. Apparently all devices need to be on the supply side of the tank in a drainback system. Dean