10 gallon tank, suppling 2 arms low pressure, I avg 30 to 45sec total presoak spray time PLUS dwell time so no problem. 03 nozzles about 7 to 9 gallons per vehicle depending on size. I think the heater puts out 5 gpm been a long time since I checked
the specs. When I first set up this wash I had a triple presoak wash selection (now deleted) it kept up with no problem
120deg water. Old unit, newer ones have higher flows & temp settings.