Clearing/replacing a holding tank vent...

[VanIslandGuy]

Just got back home from a nice two week cruise. Unfortunately on day five I noticed that the forward head would start bubbling after being pumped dry once the tank was more than a third full. The joker valve is new, and the water coming back is clean and odourless.

I take a look at the tank and see it is expanding very slightly like a balloon. Oh oh... Ten minutes going through this sites archives and I'm pretty sure I'm dealing with a blocked vent. I'm frustrated as hell though as I had replaced the vent line this year.

The blockage is in the bronze tank top vent. Thankfully I've had zero odour issues, (solved that last year with Zaal and Odorlos). I managed after about an hour with a coat hanger bent with some vice grips to push a hole through the sludge. When we bought the boat we knew the tank had over filled once.

I've done the garden hose thing at the hull vent with limited success. I've got the tank completely empty right now. I've been shooting simply green into the vent hose hoping this will break down the remaining solids at the top of the hose. I need to have the product I use in a pump type sprayer in order for it to be shot in the hull vent.

My plan was to do this every day for 3-4 days, followed by flushing the vent line again with hose water. If this doesn't work, is it possible to remove those tank top bronze elbows with hose barb and replace the whole thing?

Any suggestions or comments on fixing this issue would be welcome. Especially if there is a better product than simply green to use for this.

 

[Ron20324]

You probably have a 1/2 or 5/8 vent hose. If it connects to the tank and a thru-hull, then that further reduces the effective vent size. Best idea- if you can do it- is to put a larger vent hose in- at least an inch (I did 1.50). You need a larger tank fitting and the thru-hull. The thru-hull can be a regular mushroom-type, not the "usual" one with a screen in it. The larger size allows sticking a hose INTO the thru-hull and get the pressure pushing against the blockage. It has been a good improvement along with teeing the head intake into the sink drain.

 

[Ralph Johnstone]

I've done the garden hose thing at the hull vent with limited success.

Check to see if you have a loop before the vent hose hits the vent thru-hull.

Had one on my holding tank right from the factory. Serves no purpose, as sea water entering the holding tank through the vent is a non-issue. Removing the loop enables easy rinsing of the vent line with a garden hose, while using a rag to seal around the opening.

 

[Peggie Hall HeadMistress]

Any suggestions or comments on fixing this issue would be welcome. Especially if there is a better product than simply green to use for this.

Unfortunately the only "product" that will clear a holding tank vent is elbow grease.

The blockage is in the bronze tank top vent.
I'm not sure whether you're referring to the vent fitting on the tank or the thru-hull.

99% of all vent blockages occur at the through-hull. Dirt daubers build nests in the opening, insects fly or crawl in, get stuck and die, dust, dirt and pollen clog screens in the thru-hull.. On sailboats, however, heeling can send tank contents into the vent line, also creating a blockage at the tank in both that end of the vent line and the vent fitting on the tank. Overfilling the tank can also cause this on any boat.
So, since most blockages do occur in the through-hull, that’s the first place to look. Blast with water; if that doesn’t remove the blockage, use the tip of a screwdriver or ice pick--whatever works to scrape it out. Knock out any screen; screens cause more problems than they prevent or solve. If that doesn't solve the problem, remove the vent line from the tank and scrape out that end of the hose and the vent fitting on the tank...and by the way, it would be a very good idea to open the deck pumpout fitting cap to relieve any pressure before disconnecting any hoses!
The easiest way to prevent future vent blockages is to replace the vent thru-hull with an open "bulkhead" or "mushroom" thru-hull that you can stick a hose nozzle up against to backflush the vent line every time you wash the boat and/or pump out.

Cease use of the toilet immediately if it starts "burping" or spitting up, or if a manual toilet begins to get harder to pump.
Continuing to use the toilet against a blocked tank vent will pressurize the system, resulting in a geyser when you open the deck pumpout cap if you're lucky, a burst tank if you're not. Do NOT attempt to pump out if the vent is blocked...you won't be able to because the pump will pull a vacuum that'll prevent it from removing more than gallon or two. An especially strong pumpout can implode a tank.

 

[VanIslandGuy]

The blockage is in the bronze tank top vent.
I'm not sure whether you're referring to the vent fitting on the tank or the thru-hull.

Hi Peggie,

The vent hose, and through hull fitting are venting fine, (that was fixed last fall). It is the actual bronze elbow that is on top of the tank where the problem is. I've done the elbow grease method, (coat hanger bent to follow the curve of the fitting pushed repeatedly until it went through.) My hope is the simply green will soften the material in the clogged fitting so it will be easier to rinse out later. If there is a better product to use that you can recommend I'll buy it.

Can these bronze holding tank fittings be removed without damaging the tank? Also is it possible to plumb a new additional fitting on a white opaque plastic holding tank, (1998 Hunter 410). ie) Hole saw, and new larger diameter hose to an additional through hull. I don't want to replace the tank over a blocked fitting.

 

[Peggie Hall HeadMistress]

That fitting never should have been bronze, or any metal, because plastic and metal have different thermal co-efficients (tech speak for "they expand and contract in different amounts and at different rates"), which cause cause the fitting to leak or worse yet, cause the female fitting tank to crack. Unless it's stuck so tight you can't remove it without cracking the plastic, or someone who didn't have a clue what he was doing (that he used a bronze fittings kinda makes that obvious) used something like 5200 to seal it, it should be removable. At the very least you should be able to take the vent line off it--and you need to,'cuz just squirting Simple Green or anything else down the vent line isn't the answer...you need to scrape out the fitting and and that end of the hose. Warming the end of the hose with a blow dryer should soften it enough to let you get it off....that mgiht also soften any sealant used on the fitting. If there's buildup anywhere but the end in the vent line--which is extremely rare butt has happened--replace the vent line.

Installing another vent fitting is not only possible, thanks to a li'l gadget called the Uniseal UNISEAL it's actually pretty easy if you have access to the top of the tank. I"d replace instead of adding...cap the bronze fitting.

My book (see link in my signature) has some detailed instructions...you might consider getting a copy if you don't already have it.

 

[VanIslandGuy]

Thanks Peggie,

I agree with you on the bronze fitting, unfortunately Hunter's design team saw it differently. I'll get your book.

 

[Peggie Hall HeadMistress]

Hunter isn't alone...Even after 30 years, boat builders are still the worst sanitation system designers on the planet 'cuz they've never figured out that holding tanks have almost nothing in common with water or fuel tanks.

 

[VanIslandGuy]

Success! Got the fitting off the tank. At the fitting there wasn't even a pin hole in the "black muck". Took a while with a flat headed screw driver and a lot of pressurize water. All clear finally, the tank breathes again.

Treated the hoses through the head with muriatic acid, now everything seems to be working really well. Off to the pump out dock to flush the tank a few times.

Thanks Peggy, and great book BTW. I bought it on Kindle yesterday.

 

[Patrick Randall]

Peggie, I have your book (quite an old edition now) and can't find any reference to the Uniseal you mention. My vent is blocked and I need to install another one as the original (It's a Hunter 30T) is inaccessible. I can get to the top of the tank - how does it work?

 

[Peggie Hall HeadMistress]

The first edition of my book predates the Uniseal...it's in the newer one. See my reply to your latest post about this in the mid-size boats forum.

Success! Got the fitting off the tank. At the fitting there wasn't even a pin hole in the "black muck". Took a while with a flat headed screw driver and a lot of pressurize water. All clear finally, the tank breathes again. Treated the hoses through the head with muriatic acid, now everything seems to be working really well. Off to the pump out dock to flush the tank a few times. Thanks Peggy, and great book BTW. I bought it on Kindle yesterday.

Woohoo! Only one more thing you need to do: replace the vent thru-hull with an open "bulkhead" or "mushroom" thru-hull that you can stick a hose nozzle up against and back flush the vent line every time you wash the boat, preventing future blocked vents.