Originally Posted by thinwater
You know, the problem may be with the tank or the drain. Gravity isn't much. Do you have trouble pumping in to the tank? You only need a tiny hole to admit enough air to drain, and it sounds like you have that. Think of how small the vent is in a jerry can. Maybe not.
Like thinwater says:
If the vent was really plugged, you would not be able to pump
INTO the tank because the air needs a way to escape.
Putting air pressure into a holding tank
vent is truly a potential disaster. Don't try this at home, people! The square, flat sided holding tank
was NOT made to contain even a tiny bit of overpressure. The consequences of a split side on a full holding tank is downright scary to even think about...
Before you go changing the vent, you will want to be SURE that the drain is not clogged.
It is easy to check the vent. Just remove the hose make sure it is clear, and the fittings at either end are clear.