Clogged holding tank vent

[tcoop]

Hi all, I am looking for more ideas to unclog the black water tank vent.

Diagnoses: Smell after flushing inside. I assumed it was the vent and got a long tip air gun and took the compressor to the boat, hoping to blow out the clog. Before I started blowing I did remove the pump-out lid and I could hear the air rushing in as I unscrewed it, so no working vent.

Removal: Repeatedly tried to blow out the clog with the air gun without success. The air would build up in the hose until I pulled the air gun tip away and then air would flow back out through the vent. I also tried a fishing a wire through the vent and only got about a foot in due to resistance of the bends. The through hull is 90 degrees straight up.

Ideas: This is where I looking for help. First thought is to use a hose to get water in the vent line to soften the clog. I don't expect the water pressure to be better than the air pressure was but if it could soften or loosen possibly. Second idea is to cut the vent hose in the middle remove the clog mechanically and then put the hose together with a barbed coupler. Advantages of this are reasonable working space, both ends of the hose are difficult to get to. Other ideas?

Thanks Tim

 

[O C Diver]

Deleted

 

[O C Diver]

Try getting a pumpout. A clogged vent hose won't allow the tank to be pumped out.

Ted

 

[Comodave]

Be careful when pumping out with a clogged vent, you can collapse the tank. And that is way worse than just dealing with a clogged vent. Do you have a filter in the vent hose? If you do it may be the source of your clog. I would guess if you don’t have a vent filter that the clog is close to the rank from stuff getting sloshed up into the vent and then drying out. Do you have any access holes in the tank? Like a screw out access plate for the holding tank monitor.

 

[HeadMistress]

The vent thru-hull and the other end of the vent line (that end of the hose and the vent fitting on the tank) are two most common locations for a vent blockage. Compressed air is unlikely to clean out either one...the blockage is a buildup of tank contents in those two places that'll have to be scraped out. Though not impossible, its very rare for a blockage other than a large insect to occur anywhere else in the vent line.

Start by cleaning out the thru-hull...use a screwdriver blade, ice pick--whatever works. If that doesn't result in a spew out the vent (it won't 'cuz you've already relieved any pressure in the system) you'll need to relieve the pressure before removing the vent line from the tank to clean them out...so open the deck pumpout fitting VERY CAREFULLY with a hose at the ready. Be sure you're UPwind of it! Scrape out that end of the vent line and the vent fitting on the tank...reconnect the vent line.

If there's a filter in the vent line, remove it...once a filter gets wet--which can happen when a tank is overfilled or even due to heeling--the charcoal swells and blocks the vent...one of the reasons why vent filters aren't recommended for use on most sailboats.

You mentioned bends the vent line...straighten it out! In fact, it would prob'ly be a good idea to replace that line. Use sanitation hose...the least expensive Shields or Trident #148 is ok for vent line.

To prevent future blockages, replace the "vent" thru-hull (designed to keep sea water out of fuel and potable water tanks, but boat builders use 'em on all vents) with an open bulkhead or "mushroom" thru-hull...it doesn't matter if a little sea water gets into a waste tank. This will allow you to put a hose nozzle against it to back flush the vent line every time you wash the boat and/or pump out.


--Peggie

 

[tcoop]

Thanks for the quick replies.

The boat is a 37' Nordic Tug. The tank is part of the keel, 40 gallons. There is only 2 gallons of liquid in the tank since last pump out. There is no filter in the vent.

The plan is to replace the through hull at next haul out based on reading previous threads. The mechanical surveyor mentioned that the vent had the charter modification when we bought the boat. The charter mod is a hole drilled in the middle. It is all SS with a round center, now with a hole slightly off center. I tried to upload a pic but to no avail.

I will post updates as I know more.

 

[Roger L]

I drilled mine out got rid of the screen. I pumped some Simple Green in there a couple of times let it sit and was able to pass water to the tank.

 

[SteveK]

Tcoop
You have not said if you checked the vent exit from the tank. As Peggie said, one of two places when no filter involved that gets clogged.
I can add mine was clogged there.

 

[Bacchus]

I did not have a clogged vent on mine but the small size, and long run made mine ineffective. lack of access to the thru-hull made replacement impossible. I ended up abandoning my old vent completely and ran a new larger straighter hose and straight mushroom thru-hull per Peggie's recommendation and where I had access to both ends.

In some cases it might be possible to add an access plate for vent fitting / hose replacement / maintenance.

 

[healhustler]

Tcoop
You have not said if you checked the vent exit from the tank. As Peggie said, one of two places when no filter involved that gets clogged.
I can add mine was clogged there.

Double ditto for me. One night while we were anchored out, a strong odor got me worried about the waste tank level. I pulled the vent line from the top of the tank and tried to stick a pencil down through the fitting to see if the level was detectable by the pencil. When I tried to put the pencil through the fitting it was blocked by a hard gray matter which I assumed must’ve been crusty “residuals”. Like Peggy noted above, I just took a screwdriver and chiseled the area clear. No issues since.

 

[Comodave]

I added 2 1.5” vents to our holding tank this winter, one out each side. I found the factory installed vent filter the other day. It is in an area that is impossible to replace it. And it looks like it is still the OEM filter, never been replaced and the boat is a 1998. Wonder how effective it was…

 

[HeadMistress]

I added 2 1.5” vents to our holding tank this winter, one out each side. I found the factory installed vent filter the other day. It is in an area that is impossible to replace it.


I'm guessing that vent line is no longer in use....???


--Peggie

 

[tcoop]

I have not tried to get to the tank connection yet, all I have done is at the through hull end. I am not sure I will be able to fit into the space but will give it a try Tuesday.

 

[DCDC]

Our aft holding tank vent line has a tee with a capped garden hose connection for flushing. Have never needed it but I assume a former owner had some problem and installed an easy way to put some water pressure on the line.

 

[HeadMistress]

Our aft holding tank vent line has a tee with a capped garden hose connection for flushing. Have never needed it but I assume a former owner had some problem and installed an easy way to put some water pressure on the line.

You and the former owner are only addressing how to "fix what breaks" instead of prevention, which is almost always simpler, less expensive, and in this case, also solves another problem:

Remove the tee and garden hose connection--which wouldn't clear a blockage at either end of the vent line (thru-hull and connection to the tank)--anyway--and replace the "vent" thru-hull with an open bulkhead aka "mushroom" thru-hull. This allows you to PREVENT vent blockages by putting a hose nozzle against the thru-hull to back flush the vent line every time you wash the boat and/or pump out.

The open thru-hull also does something "vent" thru-hulls can't do: increases the air exchange with the gasses in the tank, helping to create the aerobic environment in it necessary to prevent odor.

--Peggie

 

[Comodave]

Peggie,
I don’t know how well the old vent line with the 24 year old filter worked. We bought the boat last August and really didn’t use the head much and only pumped out once before we hauled the boat. But I wasn’t sure if the boat had a filter or not. Last week when I had to replace a bad solenoid for the windlass I happened to look up and saw the filter. I don’t know how Formula though anyone could ever replace it.

 

[tcoop]

So the clog is removed. Since I was sure that the through hull was clear I started at the tank end. First learning is that boat spaces are not made for tall fat boys to get into. I would have given a pot of gold for a leprechaun. Hose removed, no blockage, no debris and no air through the hose. On to the through hull, removed the hose it was clear, after a little work it was clear. I did find a plastic stick with thread as a lanyard (6") by the hose that fit perfectly in the hole that was drilled in the vent previously.

I am happy that the clog is removed but I am disappointed that it wasn't a major plug that I could hold up as a trophy. This was the first time I was able to use a heat gun to heat the hose to get it back on. What a great thing I don't think I would have gotten the hose on the through hull without heating due to not having leverage.

I noticed a little rust color on the outside of the hose near the through hull and ignored it. While tightening one of the clamps with a nut driver, the clamp broke in half. If you see rust stains on your hoses pay attention. Luckily I had a spare.

Thanks to everyone for the advise and suggestions.

 

[Comodave]

I only use either AWAB or ABA hose clamps. They are all 316 S/S. Non perforated bands and the edge of the band is rolled so it won’t cut the hose. They are more expensive but worth it. I keep a box with different sizes on board and replace any existing clamps that exhibit any rust or corrosion.

 

[CharlieO.]

I only use either AWAB or ABA hose clamps. They are all 316 S/S. Non perforated bands and the edge of the band is rolled so it won’t cut the hose. They are more expensive but worth it. I keep a box with different sizes on board and replace any existing clamps that exhibit any rust or corrosion.

I'll have to look into those. Where do you source them from? I would to swap out all my hose clamps and double up on the necessary ones.

 

[Comodave]

I usually get them from Defender or Jamestown but they are available other places too. They sell a kit that has a bunch of sizes and a flexible driver to tighten them. The screws are metric, maybe 7 mm. But they are surely nice clamps.

 

[C lectric]

The clamp heads are indeed 7mm. I now have one more nut driver + a 7mm socket just in case.

I usually use the Tridon clamps I have used for the last 40+ yrs. However I was rehosing my RWP as the pld part number piece with the slight angle in it is NLA. I had to use silicone hose to allow me to tweak the hose into place. 'Twas a good size discussion with the pump.

So I bought the AWABS for the silicone hose's sake. Good clamps though.

My usual sources could not supply so I tried the small more truck and light industrial oriented parts place and they had them. Ask around.

I found they number the Awabs the same as the Tridons for the hose sizing.

 

[RobbGrrr]

Mine was clogged recently.
I sprayed water into it; right through the screen. It took a few minutes, but the crud stopped coming out my end of the vent and I was through.

Double-check to make sure you have the right vent, and NOT a fuel tank vent... Close call for me!

 

[billdomb]

. I assumed it was the vent and got a long tip air gun and took the compressor to the boat, hoping to blow out the clog. Before I started blowing I did remove the pump-out lid and I could hear the

Thanks Tim

YEE HAH. Our captain had the same ideer. Used a scuba tank with an adaptor.

Blew off the top of the holding tank. Well, not entirely. Nice crack at the edge running around 9 inches.

Several thousand bucks in fiberglas work later, problem is solved.

 

[rgano]

As I was reading this, an idea popped into my mind about a possible clog removal method. Perhaps Peggy will have a thought or two on it. My idea is to fashion a connection at the end of a garden hose which will allow the connection of a length of thin, stiff nylon tubling like is used for icemaker water supply lines. I could see shoving this rig down the vent line from the hull vent end and then turning on the shore water pressure to jet through the clog while allowing the excess water to exhaust back up and out the vent - be sure stand to the side.

 

[Comodave]

As I was reading this, an idea popped into my mind about a possible clog removal method. Perhaps Peggy will have a thought or two on it. My idea is to fashion a connection at the end of a garden hose which will allow the connection of a length of thin, stiff nylon tubling like is used for icemaker water supply lines. I could see shoving this rig down the vent line from the hull vent end and then turning on the shore water pressure to jet through the clog while allowing the excess water to exhaust back up and out the vent - be sure stand to the side.

Don’t do this if there is a vent filter.

 

[jgwinks]

I usually get them from Defender or Jamestown but they are available other places too. They sell a kit that has a bunch of sizes and a flexible driver to tighten them. The screws are metric, maybe 7 mm. But they are surely nice clamps.

Right, 7mm socket or nut driver. The regular US made ones are 1/4" or 5/16". I prefer to use a nut driver or even a socket wrench to tighten hose clamps, much easier than a screwdriver especially when you can only get one hand on it which is so common in the confined spaces of a boat. For the regular type clamps I use one of the four-in-one screwdrivers that Harbor Freight used to give away free. (About $3 now.) I long since have lost the bits for it but the two ends of the bit holder are just right for hose clamps. The action on these better clamps is quite stiff and they're harder to turn than the regular type, a better driver helps a lot. I get my clamps from a local industrial hose shop.

 

[jgwinks]

YEE HAH. Our captain had the same ideer. Used a scuba tank with an adaptor.

Blew off the top of the holding tank. Well, not entirely. Nice crack at the edge running around 9 inches.

Several thousand bucks in fiberglas work later, problem is solved.

Scuba tanks are like 3000psi. Not surprising.

 

[jgwinks]

Mine was clogged recently.
I sprayed water into it; right through the screen. It took a few minutes, but the crud stopped coming out my end of the vent and I was through.

Double-check to make sure you have the right vent, and NOT a fuel tank vent... Close call for me!

About the only "vent" fitting your going to find is a fuel tank vent. Has screens to keep bugs out, and as a spark arrestor for gasoline. You absolutely don't need or want a screen on a holding tank vent. A regular mushroom type through hull is much better, won't clog as easily and you can clear it with a shot from a water hose.

 

[rgano]

Don’t do this if there is a vent filter.

Goes without saying. Oh, you did.

 

[Comodave]

You never know when someone will take you literally…