I've always thought that it would be a worthwhile investment in plumbing in with a T one of the no longer used sprinkler valves (if you have the old style system) into the intake line and the also teeing the other side into the vent/drain line and putting it on a switch up in the dash somewhere. That way if you had problems priming the system you just open up the sprinkler valve from the dash without having to climb into the motor compartment and let it vent until you get water flowing and then close it back up to fill up the sacks. Instant priming without leaving the drivers seat.