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post #1 of 12 Old 03-16-2010 Thread Starter
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holding tank vent

I will be installing a holding tank where the inboard engine used to be on my 1966 Bristol 27. I was wondering where would be the best place for the vent(s). I am new to this boat rebuild process and would love to hear from you all. The tank will be 20 - 25 gallon. I think that anywhere near the cockpit would create a smell issue. I have seen pictures of this type of sailboat and she likes to heal. So anywhere near midship might cause a problem with egress of water. Thank you all for any help.
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post #2 of 12 Old 03-16-2010
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The usual spot for holding tank vents is a few inches below the toe rail on the freeboard. It is important to have the vent holes near the tank so the vent hose is kept short. When we replaced our tank we added a second air vent to the tank as the more air in there the less stink is created. We use the KO bacterial tank treatment and have never smelled the tank while sitting in the cockpit.
Midships is probably not the best location for the vent(s) for the reasons you mentioned.

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post #3 of 12 Old 03-16-2010
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Quote:
Originally Posted by tugboatdon View Post
I have seen pictures of this type of sailboat and she likes to heal. So anywhere near midship might cause a problem with egress of water.
I gather you mean ingress of water when the boat is heeling. You could run a vent line out through the transom I guess. That would work ok except possibly with a following breeze, just keep it an adequate amount above the waterline.
Why are you locating the holding tank so far from the head? At least I assume it's farther than necessary.

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post #4 of 12 Old 03-16-2010
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First, the vent should be 1" hose according to Peggie Hall, the doyenne of marine heads. It should be terminated in a standard through-hull. It should be as short and straight as possible, to maximize ventilation of the holding tank.

If the tank is well aerated, then the stinky anaerobic bacteria will be reduced and there will be little odor.

I would ask where the head in the boat is. If the head is forward in the boat, it is a really bad idea to put the holding tank aft. The longer the distance between the tank and head, the more hose that will be sitting full of waste, unless you use a lot of water to pump the hose clear, and the more likely the hose will permeate. Also, the more waste that will leak into the boat if you have to disconnect the hose at any time. Keeping head waste hoses as short as possible is generally a good idea.


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Originally Posted by tugboatdon View Post
I will be installing a holding tank where the inboard engine used to be on my 1966 Bristol 27. I was wondering where would be the best place for the vent(s). I am new to this boat rebuild process and would love to hear from you all. The tank will be 20 - 25 gallon. I think that anywhere near the cockpit would create a smell issue. I have seen pictures of this type of sailboat and she likes to heal. So anywhere near midship might cause a problem with egress of water. Thank you all for any help.

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post #5 of 12 Old 03-28-2010
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ADVICE WANTED
I have similar questions about venting a holding tank. I'm in the final stages of a new holding tank installation; my tank was built with two vents but my mechanic has very different ideas than I do about the location and number of vents ... I would welcome some advice to resolve our impasse:
* Specifically, he wants to plug up the aft vent on the tank rather than go forward with two vents.
* As for the forward vent through-hull, he's concerned about siphoning, so he wants to run the vent hose in a loop above the through-hull before connecting rather than doing a straight run from the tank opening to the through-hull.
* In addition, he's inclined to locate the single vent through-hull on the side of the main cabin to reduce the risk of siphoning.
* As for me, I've been inclined all along to think there should be TWO vents, to run the vent hose in a straight path to the through-hull, and to locate them just below the toerail.
----------------
I appreciate any advice people may have to offer--

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post #6 of 12 Old 03-28-2010
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Quote:
Originally Posted by good5buck View Post
ADVICE WANTED
I have similar questions about venting a holding tank. I'm in the final stages of a new holding tank installation; my tank was built with two vents but my mechanic has very different ideas than I do about the location and number of vents ... I would welcome some advice to resolve our impasse:
* Specifically, he wants to plug up the aft vent on the tank rather than go forward with two vents.
* As for the forward vent through-hull, he's concerned about siphoning, so he wants to run the vent hose in a loop above the through-hull before connecting rather than doing a straight run from the tank opening to the through-hull.
Really bad idea... will basically stop any air flow and cause the tank to load up with anaerobic (stinky) bacteria.
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* In addition, he's inclined to locate the single vent through-hull on the side of the main cabin to reduce the risk of siphoning.
* As for me, I've been inclined all along to think there should be TWO vents, to run the vent hose in a straight path to the through-hull, and to locate them just below the toerail.
Good idea, provided they're actually two separate vent lines with separate tank openings. Maximizes the airflow through the tank and helps promote the low-stench aerobic bacteria.

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post #7 of 12 Old 03-28-2010
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I have had good luck with using two vents on my forward mounted tank. The key to your heeling question is to install the vent ports on the extreme port and starboard top edges of the tank,. When installing the vent hoses, criss-cross them. Lead the port port (hehehe) to starboard and vice versa. This will keep the vent port on the high side of the vent hose that leads down hill to the sea.
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post #8 of 12 Old 03-28-2010
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One more question, but first some background .....
My tank is configured with two separate dip top-mounted tubes and discharges that lead to (a) a manual Whale diaphragm pump and (b) a deck pumpout fitting.
In this case, my mechanic is pushing me to put a ball valve between the tank and the diaphragm pump to improve suction and protect the manual pump. I haven't seen this approach recommended anywhere else under the sun, although it doesn't strike me as a terrible idea. Thoughts?
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post #9 of 12 Old 03-29-2010
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that is not a bad idea. If you left the seacock to the manual pump's discharge line open by accident and didn't have this ball valve your mechanic is suggesting, you could easily damage the pump's check valves when you pump out the tank. If the vent to the tank was restricted or clogged, this becomes almost guaranteed.

This is the same reason I recommend putting in a diverter valve rather than just a "Y" when setting up a manual pump to dump the holding tank overboard.

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One more question, but first some background .....
My tank is configured with two separate dip top-mounted tubes and discharges that lead to (a) a manual Whale diaphragm pump and (b) a deck pumpout fitting.
In this case, my mechanic is pushing me to put a ball valve between the tank and the diaphragm pump to improve suction and protect the manual pump. I haven't seen this approach recommended anywhere else under the sun, although it doesn't strike me as a terrible idea. Thoughts?

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a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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post #10 of 12 Old 05-21-2010
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I installed a Ronco tank a couple of years back. It came with one 1/2" threaded vent fitting on a side near the top and two 1.5" threaded fittings for inflow and outflow. I'd like to increase the size of the vent to 1", as recommended, and add another vent to the other side of the tank. My question is how to add another vent without adding an access panel to the top of the tank. Is there a way to thread a new fitting from the outside only? I don't know the thickness of the tank walls, unfortunately, but maybe someone out there has some knowledge/expertise at this?

TIA
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