Holding Tank Vent

[zman18]

Anyone have any suggestions on the best way to clear a blockage in the holding tank vent? Thanks

[Tim OSullivan]

You will be surprised at how deposits build up even in the vent hose so I replaced the hose and removed the external vent for cleaning. It's a pretty tight area above the head, if you replace the hoses save yourself some frustration and use a heat gun to install the new hoses.

Tim

[zman18]

Tim,
Were you able to replace the hoses without removing the entire tank assembly? The space seems pretty tight to do anything near the top of the tank.
Thanks
John

[nybor]

Hi. I replaced my holding tank vent tube. Pretty easy. You have to pop out the two (maybe three) wooden dowel plugs that hide the wood screws holding the little wooden railing on (above the access door). Then cut (exacto) the sealant around the white panel (vertical) and unscrew the screws holding it in place. Removing those two items lets you get easy access to the tubing.
dave

[zman18]

Dave,
Thanks I saw that area above the tank but hadn't tried to open it yet. I'll give it a try.
Thanks
John

[TBOT422]

You may want to try to 'backflush' the vent tube before disassembling everything. Place a garden hose against the vent on the outside of the hull. Try to seal it as best as you can with rags and pressure from your hands. Have someone else turn the hose on and try to back flush fresh water thru the vent line. You will want to have the pump out fitting removed so that air can come out of the tank. I believe there is a screen on the hull vent fitting, it can become clogged with salt residue (possibly sailing with the rails in the water?). Normally, unless the tank has become overfilled there should not be waste in the vent tube, although I can attest to the fact that most toilet paper floats to the top and when overfilled, the vent tube will get clogged with toilet paper.

What kind of symptoms make you think the vent is clogged?

I've had the panel above the tank removed when I replaced the discharge hose. It's pretty cramped area, but if you need help or moral support, let me know.

[keeljoy]

Can you snake the vent from the side of the hull?

Keel Joy hull #211

[wcconway]

Performed a scientific test on the Holding tank today because only 5-6 flushes appear to fill it up. Background: after a pump out in which only a few gallons are pumped out and it appears to be empty befause nothing else will come through the pump out hose. However, when trying to back flush the tank with fresh water the tank will only hold a couple of gallns before overflowing. Lately, if the deck cap is slowly unscrewed ever so slightly a lot of air escapes. We also noticed a bulging tank behind the head after just 6 flushes. We use fresh water from the shower hose to flush so we are very aware of how much flushing water is being used. We also never allow toilet paper into the head. It is disposed of separately.

So the scientific test today while offshore was to open the thru hull valve for a little while to ensure the tank was empty. Closed the thru hull behind the head Then we took the wash down hose, a gallon milk jug and a long funnel to see how many gallons we could pour into the deck opening before overflowing onto the deck. It took only 4 gallons before overflowing. We left the deck cap off, opened the thru hull behind the head and left the washdown sprayer wide open into the tank from the deck for 10 minutes and it never overflowed. That should indicate that the tank was in fact emptying. Right? Next we closed the thru hull and again could only get 4 gallons into the tank from the deck fill.

Suggestions? Remedies?

[KenKrawford]

Hi Wally & Connie,

Your "symptoms" suggest a couple of possibilities to me. The bulging tank strongly suggest that the vent is blocked. Since you've posted this under the title of "Holding Tank Vent", I assume that you've checked that. When your tank is empty and you're still connected to the pump out station, you should hear air being sucked through the vent on the side of the hull. Check the holding tank at this time - does it appear slightly concave? If so, your vent is blocked. You may have to disconnect it at the tank and flush it out. There is a screen inside the scoop where the vent exits the hull. This makes it a bit difficult to flush it from the outside inward.

[zman18]

I just went through this on my boat. Ended up removing the vent hose from just the waste tank fitting. Then using a small "snake" (wire hanger) to ream out the hose. I also did this from the outside vent to remove a blockage. This seemed to solve the problem. The hardest part is working in the tank area. Its a real small space and hard to get your hand it to get the hose back onto the waste tank.

[AynB]

Just to add to the discussion. The holding tank vents are the same devices that vent(drain) the LP tank cockpit areas. I've disassembled the two on the stern a number of times as neither propane nor water was draining. There is a small circular wire screen inside the actual vent, that collects a lot of small hairs, dust, mites and spiders and can be a bear to clean. More than once, I have wished for the type of holding tank vent that is plumbed into a stanchion. Never had one of those get clogged yet.
al