Holding tank air lock...

[ancora]

Had a holding tank air lock while on a Memorial Day raft-up. I removed the pump out cap and air whooshed in and the pooper worked. The vent line from the tank takes a downward slope and then goes up to the vent. Could this be the problem?

 

[SCOTTEDAVIS]

Yes, if the tank was full and the boat rolled a bit of slosh could have surged up into the line leaving behind ....well ... stuff and when it dried it could easily cause a clog.

Also look carefully at the outside the hull vent it often has a small screen that can be clogged with corrosion or even a bug nest, clean that sucker out if found and consider replacing the hose and thru-hull with a 3/4 inch line for better air flow, the aerobic bacteria will be happier and they eat the anaerobic bugs that cause the smell.

Use a 3/4 inch hose thru-hull like you would a bilge pump discharge.

I really recommend Peggy Hall's book she is the "Head Expert" regarding...ummm stuff.

 

[Steve]

The low spot could hold water, or the vent might be plugged with crud build up or mud dauber nest, spiders love them too.
good luck!

 

[Conall63]

The vent line should have constantly grade back to tank with no dips to hold water. Condensation could be enough to fill the low spot and air lock the line.

Conall

 

[FF]

Air in the holding tank seems to be a big factor in lowering the onboard stink.

If you are changing , most RV use a 1 1/2 vent line and have few stench problems.