Holding Tank Vent

[Peggie Hall]

To my knowledge, Catalina is the only sailboat builder to run vent lines into rail stanchions...and even they have finally figured out what a bad idea it is--at least when it comes to the holding tank vent--and have started putting in vent thru-hulls.  And that's what you need to do: move the vent line to a thru-hull. Install an open bulkhead or "mushroom" thru-hull, not a "vent" fitting in a location on the hull that will give you the shortest, straightest most horizontal run possible without putting it below waterline. That's gonna put it a bit higher than the optimum obviously....prob'ly somewhere near the toe rail.  Put a clamshell over it to prevent taking on any water when the rails are in the water.

[Roger Patterson]

Running a new line from the holding tank to a vent just under the toe rail resolved my problem of a clogged vent line thru the stanchion. I also added a tank monitor at the same time. You would be absolutely amazed at the built up pressure in the tank when pump out deck plate was opened. I leave the rest to your imagination.

[Peggie Hall]

Another reason to use an open bulkhead fitting instead of a "vent" fitting: the open fitting makes it a LOT easier to make sure the vent never becomes blocked by backflushing it every every time you pump out and/or wash the boat.

[Kelley Dean]

These discussions have been so informative. Thanks again Peggy for sharing all your knowledge with us. So................what is the best vent hose and mushroom thru hull size? Do want to go bigger. Does anyone have a picture of what the mushroom fitting looks like installed just below the toe rail?

[Peggie Hall]

On a 34' boat, a 1" thru-hull will look just fine.

[Stu Jackson]

What'd be really, really nice, would be for someone who has done this to post a photo.  Once I get back from our trip, I plan on doing this, along with installing our new Raritan PHCII.  Hope someone can beat me to it.

[dbpaul]

An example.....untill Stew gets back.

https://picasaweb.google.com/1dbpaul/20110307#5581388166050291042


https://picasaweb.google.com/1dbpaul/20110307#5581387638156512674


paulj

[Lance Jones]

I'd really like to do this too. Can someone do a wiki on this? I'm a picture type of guy... Thanks again Peggie for all the advice.

[Exodus]

I am planning on doing this as well.  PO of my boat rerouted the vent all the way to the stern with an undersized hose (smaller than factory hose).  I was going to connect it back to the stanchion until I determined the stanchion was filled with silicone. 

So I decided if I am either going to have to pull the stanchion to clean it or drill a hole for a new vent, might as well drill a new hole.

Now my question is where do I locate said vent?  I would like to put it on the port side of the hull just below the waste fill deck plate, but worry about water intrusion while heeled over.   Anyone located a vent in this location?

[Peggie Hall]

Now my question is where do I locate said vent?  I would like to put it on the port side of the hull just below the waste fill deck plate, but worry about water intrusion while heeled over. 

I wouldn't put it directly below the deck pumpout fitting...for one thing, you have a pumpout hose in the way.   Put in anywhere along the side that will allow you to run a 1" hose in a straight line that's no longer than 5' (shorter is better) up to the toe rail, rising no steeper than 45 degrees.  Put a clamshell cover over the thru-hull to keep water out when your rails in the water (although you'll sail faster if you learn to keep the boat more upright). That will give you an elbow on the top of the tank and hopefully just barely enough of a bend to let you use a straight thru-hull.

[scotty]

PaulJ,  Thanks for the picture.  What is the larger cylinder in the stern area?  It looks like a blower. 

[Ted Pounds]

Peggy's point to run the vent hose in a straight line is very important.   You don't want any low spots where water can collect.  If that happens then the water will block  the vent lint line (just like the trap in a sink which blocks sewer gases from coming out the sink).

[Bobg]

Getting back to introducing air into the tank, I have read the archives where the dinghy foot pump was used and a solar air pump, bubblier ect:   has anyone thought about a 12 volt air compressor some of us carry around in our vehicle? A air stem similar to a valve stem could be mounted somewhere in the system and the small hand held compressor could be activated to put air in the holding tank for a few minutes.  I dunno, just a thought.
If oxygen  is what we truly need, Seems like even putting another air vent in the tank with a short run won't pull oxygen to the tank, just the act of flushing the toilet forces air out, I mean are we relying  on atmospheric pressure to replenish the oxygen in the tank? hoping gravity drops air into the tank? I think I am missing something here.
I do pump out a lot, rerouted my vent line to ensure no low spots and use oderlos but the smell starts to occur when the tank is a little better than half full, I would like to  install a 1" vent from the top of the tank and route it out the hull like Roc has done, but I find a one inch elbow and vent line won't fit on top of the tank without hitting the under seat wood cover.  I am in Lake Superior where the water is very clean and I do have Peggies book, very good book I may add

[Lance Jones]

Bob,
I don't think the primary purpose is primarily to get O2 into the tank; but, to allow pressure inside the tank to vent out of the tank and boat. I also agree with you that a 1" elbow would be too big for my boat. Maybe stay with the same size elbow and hose and then grow it to 1" at the appropriate time.

[Peggie Hall]

Aeration has to be continuous 24/7/365 (except during winter layup of course) for it to maintain an aerobic environment in the tank. When you turn it off, the tank turns anaerobic...so you'd just be blowing smelly gasses out the vent if you only put air into the tank intermittently.

No...gravity won't drop air into a tank...and besides, the gasses created as waste breaks down are heavier than air, so they don't rise either. When the vent line is short--<5'--straight, and doesn't rise more than 45 degrees, a single vent line will provide enough exchange of air to allow aerobic breakdown. But if the vent is long or rises more than 45 degrees, passive ventilation using a single vent doesn't always work very well.  

However, the right tank product can help.  Odorlos is an organic product that actually helps to oxygenate tank contents. The active ingredient is nitrates, which promote oxygen release from organic matter (waste in this case), helping it to break down aerobically. If that's not what you're using, you might try switching to it. Just be sure to read and FOLLOW the directions!

Btw...we ARE only talking about odor out the vent?  NOT odor INSIDE the boat?  'Cuz if it's odor inside the boat, the tank isn't the source. So it won't matter how often you pump out out, or how well the tank is ventilated or any tank product will cure it.