holding tank vent line

JSmith · Post by **JSmith** » Mon Dec 04, 2006 8:17 am

I'll be installing a holding tank up forward under the v-berths on our Challenger and wonder about the vent line-

All the thru hulls lead to the transom (or below the waterline up forward if they can be submerged), and I definately don't want any thing on the hull up forward. There are two dorades where I could maybe hide a vent gooseneck. Would it be nuts (stinky) to run the line back through the cabin to the lazarette- maybe with multiple filters?

I've read about sch 40 pvc here but don't know how practical it would be to run it that far.

Thanks for any input.

dmairspotter · Post by **dmairspotter** » Mon Dec 04, 2006 9:34 am

If it's the vent line I believe that should exhaust to open air, not a through hull. On my boat, the vent line runs from the tank (under the V berth) up to the anchor well. It's open to atmosphere in there.

JSmith · Post by **JSmith** » Mon Dec 04, 2006 9:38 am

I meant to have a thru hull on the transom to open air- but it would be great to run to the anchor locker- except that is open tothe fwd berth area as well- does the filter really work:)???

Duncan · Post by **Duncan** » Mon Dec 04, 2006 11:12 am

JSmith wrote:Would it be nuts (stinky) to run the line back through the cabin to the lazarette- maybe with multiple filters?

Definitely nuts - that setup will restrict airflow and make things worse, not better. Oxygen is our friend, since it kills the stinkers (anaerobic bacteria). (That's why they have aeration ponds at sewage treatment plants).

So, it sounds perverse, but the bigger the vents, the less it will smell. Nice large vents as straight as possible to the anchor locker and the dorades sound almost ideal to promote airflow.

dmairspotter · Post by **dmairspotter** » Mon Dec 04, 2006 1:10 pm

Should have stipulated that on my boat the anchor well is isolated from the cabin and has its own dedicate drain.

On my last boat, seems to me there was a little fitting that went through the hull up near the deck join

Something like this, though I think mine was smaller

http://www.westmarine.com/webapp/wcs/st ... rtial/75/0

Summersdawn · Post by **Summersdawn** » Mon Dec 04, 2006 2:24 pm

Consider adding 2 vent lines, one to each side. That way you get cross-ventilation.

Oxygen is our friend, since it kills the stinkers (anaerobic bacteria). (That's why they have aeration ponds at sewage treatment plants).

The more air flow the better, big hoses help as well.

JSmith · Post by **JSmith** » Mon Dec 04, 2006 5:17 pm

I'll only have one tank but the anchor locker is also vented to the cabin with multiple holes in a plywood cover just fwd of the v-berths. It might make sense to replace that with a solid one which would cut down on moisture below as well as give me a place to vent to. Going to a dorade wouldn't really work- the air goes from there directly below (and if I turned it to face aft to "suck" it would be turned back at some point by some one).

Mark.Wilme · Post by **Mark.Wilme** » Mon Dec 04, 2006 9:39 pm

I would agree on the cross ventillation - can you run them through the anchor well and put one on each side of the bow like eyebrows ?

Of course I don't know how they might fair with waves breaking over the bow - could you end up with a tank full of sea water ? - dunno.

Quetzalsailor · Post by **Quetzalsailor** » Tue Dec 05, 2006 10:06 am

Presuming your Challenger is an Alden with lots of nice obstructive woodwork, like our NE 38... Our holding tank vent is forward of amidships, piped into to the vented loop concealed in the head casework. Easy to plumb, easy-ish to access.

Don't do it! And don't lead it forward or into a dorade. Since we are more likely to not be going dead downwind, I will be moving mine aft, waaay aft! More often than not, one gets an unpleasant waft when sitting in the cockpit while the other has pumped the head.

I don't think you get much 'ventilation' through any 5/8" dia hose, what you get is no 'inflation' of your tank when decomposition and off-gassing occurrs, and when you pump more waste into it. I think the only criteria is to not leave the hose with a droop causing a trap to hold water (from whatever source). Our previous boat's vent was on the transom, something like 15' aft of the tank, hose, worked fine.

Boats are not normally plumbed with ordinary PVC, I understand because of vibration and breaking. I've used CPVC on my new water system, so we'll see. Very tempting to use such pipe since it will tend to droop less and look neater, as well as be more likely to go where it's pushed when fishing behind casework.

Ceasar Choppy · Post by **Ceasar Choppy** » Tue Dec 05, 2006 11:32 am

As long as PVC is properly supported-- especially over the long runs you are talking about, it should work OK. But that is a lot of pipe!

I agree that the vent should not be in the dorades. It STINKS if your head is close to capacity -- especially in the middle of the summer-- no matter how well vented! I have a 1" dia. vent on mine with a run of 5 feet and two 120 deg bends, vented amidships just below the toe rail. I couldn't get it any better than this and it still stinks once in a while when someone flushes.

Summersdawn · Post by **Summersdawn** » Tue Dec 05, 2006 12:48 pm

The larger hose sizes help prevent "clogging" if the tank becomes over-filled, or heeling causes the vent line to fill.

JSmith · Post by **JSmith** » Wed Dec 06, 2006 6:59 am

Thanks for the input!

I think I'll look over the run back aft. The pump out will be up forward next to the sea water pressure hose so I can use that to flush 'er out.

Waiting to hear what other Alden Challengers have for a set up too.

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