Short holding tank vent hose to Stern, or longer run to aft quarter?

[sydneybadger]

I'm upgrading my holding tank vent line from 5/8" to 1" on my 35' sailboat with a sugar scoop and swim platform.

What's a better choice between:
1. A short 1-2' hose, straight out the stern, near the transom shower, with a 45-degree angle rise from the holding tank to the thru-hull, or
2. A 6' hose to the starboard aft quarter, with about a 20-degree angle rise

I know Peggy Hall recommends as short of a hose as possible... but the longer run is less of an angle, and I don't know if it's bad to vent directly on the stern.

(My holding tank is located in the stern, under the cockpit, roughly on the centerline)

 

[dlochner]

Venting out the side will all the gases to enter the slipstream and blow past the boat. Off the stern and the station wagon effect can cause the gases to be sucked back into the cockpit.

 

[Peggie Hall HeadMistress]

Venting out the transom (stern) makes it impossible for the tank to "breathe" because air can only flow OUT of the tank, which will guarantee it'll stink, bso run the vent line out the side of the boat, and I'd run it forward of the tank instead of aft. Try for a thru-hull location that'll keep the vertical rise to a max of 45 degrees and put it as far below the toe rail as possible while still keeping out of the water when heeled. That'll make the vent line a bit longer than ideal, but if it's straight, it'll allow better air exchange than you'll get with a shorter vertical vent. Also, go with a 1" vent line and open bulkhead thru-hull instead of a "vent" thru-hull.

I'll be glad to help you work out the logistics if you want to shoot me a PM.

--Peggie

 

[sydneybadger]

Thanks! This is great information and makes total sense how that will get better air exchange. I should be able to run a hose out the side, slightly forward, less than 45 degree rise. I'm planning to use a SEAFLO 1" Thru Hull which is open on the outside and has a hose barb on the inside.

My tank already has a threaded flange to which I'll screw in a 1" PVC barbed hose adapter.
Does anyone know if I can use Permatex form-a-gasket #3 on the PVC thread? (I heard you're not supposed to use teflon tape on plastic and I already have some of the permatex onboard)

 

[Peggie Hall HeadMistress]

I spent almost an hour searching for the type of "molded white plastic" that SeaFlo uses for their thru-hulls without success. You need to find out 'cuz If SeaFlo thru-hulls are nylon, it's not a good choice for an above-waterline thru-hull 'cuz nylon is not UV resistant...sunlight will turn it into powder. Use PVC or Marelon.

Tank/hose fittings are sched 80 PVC. I've always used Teflon tape, at least 3 wraps. It's only recently that I've heard warnings against using it, but never with any reason WHY--how it harms plastic...I've never had a problem with it. I like it because you can remove the male thread-barb hose fitting if you need to...,plus you can find it in any hardware store, even Walmart.

Your "flange" is actually the female threaded fitting. Be careful not to OVER-tighten the male fitting, nor more than a 1/2 turn past hand tight. Reason: In the US threaded fittings are NPT standard, which is slightly tapered..TOO slightly for the naked eye to see in the short length of fittings. Over-tightening will put too much pressure on the female "collar," causing it to crack...maybe not immediately, I've seen it take up to a year.

Btw...warming a hose a bit makes it easier to slip onto a fitting (also makes hoses easier to remove)...lubing the inside of the hose and outside of the fitting with K-Y makes it even easier. K-Y is a water soluble surgical jelly that dries out, won't leave you with a permanently slippery hose connection.

--Peggie

 

[Ralph Johnstone]

It's only recently that I've heard warnings against using it, but never with any reason WHY--how it harms plastic..

Teflon tape certainly won't affect any plastic as it's completely inert at ambient temperatures. The tape is a popular thread sealant because it's clean as opposed to pipe dope which is messy. However, Teflon tape not the best thread sealant on the block, hence you will see in commercial and industrial applications for threaded pipes carrying water, the preferred sealant is 2 - 3 wraps of thread and a very light smear of pipe dope. The most common pipe dope I've seen is Permatex #2. The combination of the two seems to be better than the tape alone and the smaller amount of sealant used makes the job much cleaner.

 

[sydneybadger]

Peggie, nice tip on checking what material SeaFlo uses. I hadn't considered the UV degradation, but that's obviously super important. I sent SeaFlo an email about it and I'll post back here if i get a reply. Now I'm thinking about just getting stainless steel for the thru-hull, won't have to worry about it cracking either.

 

[capta]

I think the decision has to be made with the consideration of which place has the least possibility of going under water when sailing.