How to Clear Blocked Holding Tank Vent ?

[Cruisin Home]

I suspect that I have a blocked holding tank vent. It is not pumping out right and guage will not go down. I went to replace filter and when I unhooked hose on dirty side I did not get that smell. We had a problem late last year when we accidentally overfilled the tank and I am thinking the vent line was clogged. Should I try and clear with compressed air?? Thoughts and or experience would be appreciated!

[gonesail]

you could always replace the vent hose if it is not too difficult.

[Paul Elliott]

I had a blocked holding tank vent, and it turned out to be the wire mesh screen on the vent fitting had become filled in. So you know what I'm talking about, here's a similar vent:

I think the screen is only needed for gasoline tank vents. I either replaced the vent or removed the screen -- it was a long time ago.

[Cruisin Home]

I think replacement of hose would be a little tough, It is quite long and goes from engine compartment to underneath the inside of cabin.

Thats why I was thinking of "blowing" it out but wasnt sure if that would result in more of a problem!

Code Brown!!!!

[YourOldNemesis]

Yeah - give the tube attached to your (full) holding tank a good blast of compressed air. Send us the photos!

[imagine2frolic]

There are hose attatchments from places like home depot. I do not know if they are small enough, but they use water to force blocked lines. Most likely it is just the screen becoming plugged after time. Bugs like to make homes there......i2f

[gonesail]

that's also a problem i have with my boat. the vent hose has a low spot between the tank and the hull vent. this is where the plug probably is .. seems like compressed air would work. also if you do a pumpout it might clear it too .. or else collapse the tank.

[DeepFrz]

the vent hose has a low spot between the tank and the hull vent

That is a problem. There should be no low spots in the run of the vent hose.

[Seahunter]

Don't use compressed air; you'll break something and the crap will just plug up the screen causing all kinds of problems. Remove the vent hose and vacuum it out. A quick trick is to stuff a water hose over the vent while pumping; but if the crap has dried you'll need to take your time by add a little water at a time to loosen the crap up. You won't be able to run a wire down it as there's a goose neck inside the hull fitting. Just be patient and it will come clean.

[speciald@ocens.]

I had the same problem two weeks ago. I bought a new vent (like the one above). Had to increase the size of the hole in the hull with my Dremel. I also replaced the hose back to the tank. I cleaned the discharge hoses with muriatic scid and now everything works again.

[Cruisin Home]

you guys are scaring me, maybe I will just see if I can route a new hose. Dont want a Code Brown!

[Hud3]

I've had good results from simply blasting the vent from the outside with a strong stream of water from a hose nozzle.

[perchance]

I don,t know about your part of the world but up here bugs routinely make little nests in the vents and are a pain in the A!

[Jetexas]

Can someone post a photo of what these vents look like on the exterior of the boat? Now that the mold smell has subsided, I'm starting to recognize a holding tank smell in my boat. I'm going to attempt a massive cleaning this weekend.

[rwidman]

Originally Posted by Jetexas

Can someone post a photo of what these vents look like on the exterior of the boat? Now that the mold smell has subsided, I'm starting to recognize a holding tank smell in my boat. I'm going to attempt a massive cleaning this weekend.

Someone did. It's up near the top of the page.

If there's a screen in the vent, remove it, it's not needed. Insects build nests in them and if you overfill the tank, sewage will block them. If there's a filter and it's ever gotten wet from overfilling or trying to cleat the vent line with a hose, replace it, or just do away with it and insert a piece of hose in it's place. They are not really needed and often do more harm than good.

If there's a low spot (a loop) in the vent hose, re-route it to eliminate the low spot. The low spot can collect liquids or condensation and block the vent.

I wouldn't recommend more than about 30 PSI of air pressure if you try to clear a vent hose with air. Also, you need to disconnect the hose from the holding tank or disconnect the inlet from the head so you don't pressurize the holding tank. Bad things can happen if you do that. They are not designed to be pressurized. If you have an access plate for cleeaning, removing it will relieve the pressure.