Beneteau 473 head venting

[Full Circle 473]

Just tried to pump out the master head holding tank. It didn't seam to hold much and wouldn't take much water to flush out. I was told that the vent may not be open. Does anyone know how to open the vent on the holding tank for the master head? Or even how to check if it is open?
Thanks

 

[Roland5048]

I don't know how one would close the vent. It should only be a hose running from the tank to the outlet on the hull. It is possible, however, that it is blocked. When you run water into the tank can you feel some air coming out the vent? If not, then blocked. You might try running some water backwards through the vent or take the hose off and inspect. Should be a simple fix. As if anything on a sailboat is simple.

 

[Peggie Hall HeadMistress]

An inability to pump much out of the tank, or put water into the tank is almost certain to indicate a blocked tank vent. An earlier indication is a manual toilet that's becoming increasingly harder to pump or an electric toilet that's begun to "burp" or back up flushes. Don't use the toilet again or attempt to pumpout again until the vent is clear.
Running some water backwards through the vent isn't that easy because all "vent" thru-hulls are designed for use on fuel tanks...so they're caps with pinholes in it or just a slit in the bottom...or they have screens in 'em. I don't recommend taking the vent line off to inspect, because a vent blockage is likely to pressurize the system, which will result in a spew.
90% of vent blockages occur in the vent thru-hull...so start by using an ice pick, screwdriver blade or whatever works to dislodge and clean out anything that's clogged it. Screens become clogged with rust, dust and pollen...if there is one, knock it out...screens cause more problems than they solve.
If that doesn't solve the problem, check the vent line for any kinks or sags where liquid may have pooled in it. If you don't find any, the blockage is almost certain be at the tank end of the vent line--in that end of the hose and the vent fitting on the tank. You will have to remove the vent line to clean it out. But BEFORE you do that, open the deck pumpout cap to relieve any pressure in the system! Now you won't put half a tankful of waste into your bilge if you take a hose off.
Warming a hose a bit with a blow dryer will make it a lot easier to get off the fitting. Scrape out that end of the hose and the vent fitting on the tank. Unless you've overfilled the tank enough to push undissolved TP into the vent line, that should open it up. Warm the hose again and use a little dishwashing liquid to lubricate it to put it back on.
But as long as you've done all this, now would be a great time to replace the vent thru-hull with one that you can stick a hose nozzle up against and backflush the vent line to keep it clear every time you wash the boat and/or pump out...'cuz as is pretty obvious from reading what you have to do to cure a blocked vent, preventing it is LOT easier! Use a plain ol' open "bulkhead" thru-hull (see photo)..5/8" is the standard size. Backflushing it will take care of any insects who find their way into it.
You might want to check out the link in my signature...it goes to complete "toilets and holding tanks 101" guide to installing, operating and maintaining the sanitation system and can prevent a LOT of "head aches!"

 

[Roland5048]

I knew Peggy would come to the rescue. I didn't think of the pressure in the system when taking the vent hose off.

 

[Full Circle 473]

Thanks Peggy!!! I will check it out (very carefully without pressure).

 

[Full Circle 473]

Also thanks Roland! Nothing is difficult to fix on a sailboat, it just doesn't end. But isn't that why we do it

 

[Roland5048]

It has to be a labor of love. Otherwise, it is just work.

 

[jlp0217]

Removing the deck fitting is more dangerous than removing the vent line if the vent is clogged. The deck fitting feeds from the bottom of the tank and could spill stuff on the deck. The vent comes from the top and should only release gasses (but it is inside the boad).

 

[Peggie Hall HeadMistress]

No one suggested REMOVING the deck fitting or anything else...but before even considering removing any hoses in the system, it's necessary to relieve any pressure...and the easiest way to do that is to CAREFULLY open the cap! It's prob'ly a good idea to have a hose at the ready to rinse off any "stuff"...and be sure you're downwind too!
Obviously you've never seen anyone get a faceful of waste from the vent thru-hull upon clearing the blockage that had pressurized the system or you'd know that gasses aren't the only thing in the vent in a pressurized system. And you'd better hope that the whatever is released from the vent line ISN'T inside the boat!

I've been doing this for almost 3 decades, son...I've had time to learn what works and what doesn't.

 

[Full Circle 473]

Thanks Peggy,

My plan is to open the deck cap first. ( depressurization) Then investigate the vent hose. Take off the exterior vent cover and inspect. Next find the hose on the interior. Will probably have to remove the interior cover on the holding tank to even find the hose.

 

[Peggie Hall HeadMistress]

What "interior cover on the holding tank??" Please tell me you don't mean opening up the tank!

Open the deck cap VERY carefully and hang on tight to the cap! I wasn't kidding when I said, "have a hose at the ready." However, if you haven't used the head in at least 24 hours, don't be misled if there's no pressure to relieve when you open the cap...pressure can dissipate via a worn joker valve or anywhere else in the system that allows very slow seepage of air. Otoh, assuming that's happened can give you a faceful of something you don't want --as I once found out the hard way! And when I did, I may have set a record for how fast someone could over the side into the water, shoes, watch sunglasses and all!

 

[Full Circle 473]

Diagnosed the problem correctly. Removed the vent and found it completely clogged with corrosion. Cleaned out, no mess and everything is now working great. Thanks for all the advice.

 

[Gunni]

This is a common problem. You overfill your holding tank a few times, the waste flows out your vent line during a bumpy sail, where it dries to a paper-mache plug in the vent line. When you pump out, in addition to the customary fresh water rinse and pump, take the hose to your vent port on the topside and run freshwater back into your tank via the vent line.

 

[Jackdaw]

Beneteau.. Might be a valve on the vent line. Just sayin'.

 

[Peggie Hall HeadMistress]

I've seen some really nutsy holding tank vent installations, but I've never seen a valve in a vent line on a Beneteau or any other boat.

All "vent" thru-hulls are the same size--5/8"--and are actually designed for use on fuel tank vents, with built-in spark arresters and tiny openings intended to prevent sea water from contaminating fuel or water. Boat builders use 'em on all tanks including waste 'cuz it's cheaper to buy in bulk than separate fittings for each type of tank. They're fine for water and fuel, but NOT for waste tanks because they don't allow enough air exchange to keep the tank aerobic, which necessary to prevent odor from occurring in the tank.

So the best thing you can do, short of replacing the 5/8" vent line with a 1" line (which requires installing a new fitting in the tank, but it's actually easy to do thanks to a li'l gizmo called the Uniseal UNISEAL ) is replace the "vent" thru-hull with a plain ol' open "bulkhead" thru-hull. Not only does that greatly increase the ventilation to the tank, you can stick a hose nozzle against it and backflush the vent line to keep it clear every time you wash the boat.

 

[Jackdaw]

I've seen some really nutsy holding tank vent installations, but I've never seen a valve in a vent line on a Beneteau or any other boat.

I have. From the factory. My First 260 does, amungst others. That's why I mentioned it.

 

[Peggie Hall HeadMistress]

I had completely forgotten that SeaLand (now Dometic) introduced a tank to go with their VacuFlush toilets that doubled as both the vacuum tank for the V/Flush and the holding tank. The did indeed have a one way valve in it to allow air to escape (no way would they miss an opportunity to sell a vent line filter, which would REALLY be needed in a vent from an aerobic tank!) and a separate "pressure relief valve" installed in the tank allow air in during pumpout. I dunno if it's still in production or not.

SeaLand also made a short lived version of it they called the "Sailvac" system--a tall skinny tank made specifically to fit in hanging lockers on sailboats that also could double as both a V/Flush vacuum tank and holding tank. Although it was an "award winning" design, it didn't sell well enough to remain on the market very long. I wonder if that's what was on your 260...

 

[Gunni]

Peggy, how is that uniseal fitting going to stay in place when a holding tank vent line plugs and causes over pressure or crushing vacuum? Seems like it would blow out as the weak link in the vent.

 

[Peggie Hall HeadMistress]

That can't happen. The Uniseal is a rubber grommet...you'll put a 6-8" piece of PVC pipe in it that becomes the hose fitting. It functions exactly same way as a vent line on a threaded hose barb.

And btw, as long as the Uniseal and the piece of pipe are correctly mated, and the line coming off the pipe doesn't pull to one side of it, it WILL NOT LEAK. It's the best thing on the planet to use to add or relocate a tank fitting. However, although I have confidence that it won't leak, I don't trust DIY boat owners enough to recommend using it for a discharge fitting at the bottom of the tank.