Peggy, First a shameless compliment on your book I recently purchased. I already saved the purchase price by not buying the vent filter I had in my hand last week. Also hoping your autograph will make me rich sometime in the future... I have a question on what seems to be contradicting advice I've heard on how to prevent anerobic bacteria (the bad ones) from thriving, and I hope you can straighten me out. On the one hand, I understand that a well designed passive ventilation system in a holding tank will prevent odors. By that I mean a hose of adequate diameter (say one inch)not running greater than a 45 degree incline along a distance of three feet. Two hoses would be even better. On the other hand I've heard that a mechanical pump to force air into the holding tank (at a cost of over $200) must be below the level of waste and air must flow up through the waste using a bubbler, presumably because a single column of rising air would not be adequate. If a passive system can prevent odors, why couldn't an air pump suffice even if it didn't bubble up through the waste? I now know that my current ventilation is woefully inadequate, but I'm not quite ready yet to poke some new holes in my holding tank or the hull. Has anybody ever tried sending air down the pumpout hose? I have a 13 gallon tank with a 5/8 inch vent running 14 feet up (and down and up...) to the bow and it's not getting the job done. What if I created a Y-valve setup which converted my pumpout hose to a vent when not in use? In this configuration I would run an additional vent hose from the top of the tank to a y-valve which taps into the discharge hose. This would give me an instant 1 1/2 inch vent, but the y-valve would be cumbersome to use, since access is difficult.
Ventilation of holding tank
- Thread starter Jack B19779
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Size and location of the tank is the key
Passive ventilation won't work in large deep tanks or tanks that are in locations that make short straight horizontal venting impossible...that's when an aeration system is needed. But for ventilation above the surface to work, the tank has be able to "breathe," so your idea of just blowing air into a tank above the surface won't work...it'll only force the noxious gasses out the vent. In a tank that has a 14' vent line, that's not possible. Using your pumpout line as a vent won't work either because it can't supply any air, only function as a vent. My advice: you said you don't want to, but I don't think anything short of a pricy tank aeration system will work unless you shorten your vent line by installing a new vent thru-hull that's a LOT closer to the tank, even if it has to be considerably more vertical than is ideal. Then use Odorlos in your tank. The active ingredient in Odorlos is nitrates, which promote oxygen release from the waste itself, oxygenating it and preventing odor. That should work in a tank as small as yours. If you really want to do it right, go to a 1" vent...it's not that hard to put a larger vent fitting in the tank any more, thanks a little gadget called the "Uniseal" http://www.aussieglobe.com/uniseal1.htm (scroll all the way to the bottom of each page to see how it works and pricing). If your current fitting is outboard on the tank, move it inboard...that'll prevent waste from spilling out the vent when you're heeled. A good think you didn't buy the filter...'cuz filters are "toast" immediately if they get wet...and with your vent thru-hull in the bow, that's almost guaranteed to happen. It doesn't take a lot of water at once to ruin one...just an accumulation of little splashes over a few days. Filters are also a bad choice on sailboats that are vented to allow waste to spill out the vent when heeled...that'll ruin one immediately and can also result in a vent blockage in the filter.
Passive ventilation won't work in large deep tanks or tanks that are in locations that make short straight horizontal venting impossible...that's when an aeration system is needed. But for ventilation above the surface to work, the tank has be able to "breathe," so your idea of just blowing air into a tank above the surface won't work...it'll only force the noxious gasses out the vent. In a tank that has a 14' vent line, that's not possible. Using your pumpout line as a vent won't work either because it can't supply any air, only function as a vent. My advice: you said you don't want to, but I don't think anything short of a pricy tank aeration system will work unless you shorten your vent line by installing a new vent thru-hull that's a LOT closer to the tank, even if it has to be considerably more vertical than is ideal. Then use Odorlos in your tank. The active ingredient in Odorlos is nitrates, which promote oxygen release from the waste itself, oxygenating it and preventing odor. That should work in a tank as small as yours. If you really want to do it right, go to a 1" vent...it's not that hard to put a larger vent fitting in the tank any more, thanks a little gadget called the "Uniseal" http://www.aussieglobe.com/uniseal1.htm (scroll all the way to the bottom of each page to see how it works and pricing). If your current fitting is outboard on the tank, move it inboard...that'll prevent waste from spilling out the vent when you're heeled. A good think you didn't buy the filter...'cuz filters are "toast" immediately if they get wet...and with your vent thru-hull in the bow, that's almost guaranteed to happen. It doesn't take a lot of water at once to ruin one...just an accumulation of little splashes over a few days. Filters are also a bad choice on sailboats that are vented to allow waste to spill out the vent when heeled...that'll ruin one immediately and can also result in a vent blockage in the filter.
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