Black Holding Tank slow to drain...
Our Black Holding Tank is slow to drain. Can this be caused by a bad Air Admittance Valve or a clogged vent cap or both? The tank dumps fine at first, but it eventually backs up and then very slowly...
Forum Discussion
Waste tank draining should only slow down when getting close to empty.
Sink/shower drains have 'air admittance valves' after the 'P' trap to prevent 'p' trap from getting sucked dry when draining tank
Unless a bathroom sink or shower has been plumbed to black tank no 'AAV' on black tank. Typically grey only.
Tanks that start out draining OK then slow way down are due to tank vent being blocked OR the cut-out disc was left in tank and gets sucked down to drain out let blocking it.
Garden hose full stream down vent line from roof will verify vent clear it water flows out of tank drain valve.
Floating cut-out disc...harder to get rid of
Sink/shower drains have 'air admittance valves' after the 'P' trap to prevent 'p' trap from getting sucked dry when draining tank
Unless a bathroom sink or shower has been plumbed to black tank no 'AAV' on black tank. Typically grey only.
Tanks that start out draining OK then slow way down are due to tank vent being blocked OR the cut-out disc was left in tank and gets sucked down to drain out let blocking it.
Garden hose full stream down vent line from roof will verify vent clear it water flows out of tank drain valve.
Floating cut-out disc...harder to get rid of
