Installing Vent for Holding Tank through the hull

[Mike McDonald]

Again, thanks for the great suggestions and photo's.  This really helps. 
Mike......

[cmainprize]

I just moved my vent last weekend. I increased the size to 1 inch. 
When we had the tank made last year I had them put in a bigger fitting.  The vent line goes forward into the v berth hanging/shevling locker on the port side.  This put the thru hull about 7 inches below the rail and should rarely if ever be in the water.

[Dave Spencer]

Here's my contribution to the discussion:  Starts at reply #17.
http://c34.org/bbs/index.php/topic,6861.15.html

[Ken Juul]

vent tubing installed.  Working on a teak cover to hide the part in the upper shelf.

[Roc]

Ken,
I spoke to Peggie on the phone, when I upgraded my holding tank vent.  She said don't have a 90 degree turn leading out.  It should be a soft curve leading to the thru hull.  That's why I lead the hose forward, with a gradual slope, and a large arc to the thru hull vent.

[Ken Juul]

Yes I totally agree with Peggie's advice.  The 90 is in there until I can find a 45 to reduce the severity of the turn.  Didn't have any luck with the 45 in the town were we keep the boat, will expand my search this week.

[Mike and Joanne Stimmler]

I wonder if a radius 90 degree would work or if their even available.

[Roc]

Peggie's suggestion was also not to go directly up from the tank to exit the hull, but to have the vent hose leave the tank and take a gradual slope.  Better to have a longer run with gradual slope, then shorter leading straight up.  That's why I ran the hose forward into the locker on the port side of the v-berth.  Then turned the hose, with a large arc, leading to the thru hull.  All this is hidden behind cabinetry.

[patrice]

Hi,
One thing to make shure, is that if you go horizontal with a small slope up when leaving the tank.  Is that you don't end up with a small loop.
This is what happened in my installation, and some liquids ended trap in the vent tubing while underway, and plug it.
Of course this is not an area you look often, so it had chance to start smelling.
I am rerouting this tubing and it will go up quick to prevent this to happen again.

[mregan]

Reading Peggie's book, she also mentioned if the vent was longer than 5', even run horizontal and sloping gradually, it still doesn't work to well.   I think no matter how you run it, it isn't going to be ideal.

When I get around to it, I'm going to install a fish tank bubbler.  I installed one on my C-30 last year near the end of the season.  Drilled a 1/4" hole in the tank vent line and layed 1/4" tubing in the bottom of the tank.  Hooked it up to the 120 power.  When the boat was plugged into the shore power during the week, the bubbler is percolating the holding tank which should prevent anerobic bacteria from breaking down.  This is the smelly bacteria.  Kind of a poor mans version of the Groco Sweet Tank.

Seemed to work in my C-30 but only had it in for a couple of weeks before hauling for the winter.  If it doesn't work, I'm only out about $25.00.

http://www.groco.net/00-sanitation/stk.htm

[Ken Juul]

With our holding tanks there is no easy answer.  I think no matter how it is done it will be better than the original that has 2-90° bends and 2-1/4" (if that) holes to the atmosphere.

[Roc]

Ken is right, any improvement is better than what we have.  However, if you can follow Peggie's guidelines, it would make a better system.  BTW, I seem to remember her saying that putting a bubbler system really wasn't an advantage (when she used to post on Catalinaowners.com or Hunterowners.com).  Getting fresh air into the tank to keep it aerobic, is the best and easiest.

[cmainprize]

I would not worry about the angle or length of the vent hose run ( sorry peggy) as long as you don't have any low spots where "stuff" can collect I believe you will be good. Air only moves in one direction unless you move it mechanically, from high pressure to low pressure.  considering the pressure involved friction loss and bends should not make any difference. 

[Indian Falls]

There have been numerous posts about moving the vent line but no posts following up that purport "success" or "drastic improvement".  Anyone out there who has made this modification care to weigh in with your results?

[patrice]

Hi,
I am not a specialist in the subject, but i would guess that a shorter run and as straight as possible would be better than too long to get proper venting.