Hi Peggy, We finally launched our boat and are testing the holding tank that I installed last year. You'll recall we had some discussions about the design, and I tried to adhere to your principles. While it works well in most regards, the fumes coming out the tank vent are pretty offensive, often coming back to the cockpit, and my crew (as well as admiral) are advocating giving up on the KO strategy and shifting to bleach, lemon juice, or formaldehyde. The venting system involves two 1" vents, one with a substantial cowl to provide air intake and a 24 hour exhast vent to ensure the air circulates and is removed. I am sure that the tank is getting lots of fresh air. The problem is that the air coming out is offensive. In the long run, maybe I'll have to shift the exhaust vent to under the transom, a run of about 18 feet. Then we'd get the odors only when running before the wind. Maybe I'll have to add a bubbler into the tank. What other suggestions do you have that can make our current cruise a little nicer? Ben Stavis benstavis@verizon.net
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Tank isn't getting enough O2 for K.O. to work
If it were getting enough, the waste couldn't generate any odor. So we need have some conversation about where the vent lines go--length, vertical rise, how straight (or not)...where on the hull the thru-hulls are. The easiest way to do that is by phone...I'll email you the number. Meanwhile try Odorlos instead of K.O. It often works in systems that don't get enough O2 for K.O. to work. Afterthought: Where has the K.O. been stored? When you bought it, you didn't leave it in your car so you wouldn't forget to take it to the boat, did you? Or keep it in a dock locker in the sun? 'Cuz temps over 100 will kill the bacteria in it.
If it were getting enough, the waste couldn't generate any odor. So we need have some conversation about where the vent lines go--length, vertical rise, how straight (or not)...where on the hull the thru-hulls are. The easiest way to do that is by phone...I'll email you the number. Meanwhile try Odorlos instead of K.O. It often works in systems that don't get enough O2 for K.O. to work. Afterthought: Where has the K.O. been stored? When you bought it, you didn't leave it in your car so you wouldn't forget to take it to the boat, did you? Or keep it in a dock locker in the sun? 'Cuz temps over 100 will kill the bacteria in it.
Holding Tank Odor
I finally solved the odor prob on my tank with an in-line filter in the vent hose. I got it from West Marine. It was pricy, about $75. It will last for a long time as long as you don't overflow your tank and push the tank juice through the filter. Rumor: I have been told that virtually any in-line charcoal filter, such an ice-maker filter available at home supply stores, will do the job. However, these filters are water activated, so you have to run water through them to activate them, then drain them and install in the vent line. I can't vouch for the other filters, but the holding tank vent filter I got from West Marine works.
I finally solved the odor prob on my tank with an in-line filter in the vent hose. I got it from West Marine. It was pricy, about $75. It will last for a long time as long as you don't overflow your tank and push the tank juice through the filter. Rumor: I have been told that virtually any in-line charcoal filter, such an ice-maker filter available at home supply stores, will do the job. However, these filters are water activated, so you have to run water through them to activate them, then drain them and install in the vent line. I can't vouch for the other filters, but the holding tank vent filter I got from West Marine works.
Why vent filters are a bad idea
I wish I could put a product on the market that creates the very problem it's sold to solve...that's what a holding tank vent filter does. Oxygen is the key to odor elimination...when organic matter breaks down aerobically (oxygenated), it doesn't stink...it's only when it breaks down anaerobically (without oxygen) that it can create noxious hydrogen sulfide gasses. A filter traps those gasses, but it also prevents any exchange of air through the vent line, causing the tank to become anaerobic/stinky. So not only do they create the problem they're sold to solve, but they're also VERY expensive. They only last a year at most...are toast immediately if they get wet--which is almost impossible to prevent on most sailboats, because even a half-full tank spills into the vent line when the boat is heeled. And when the charcoal gets wet it swells, creating a blockage that leads to a pressurized tank and the disasters THAT can cause. Icemaker water line filters are designed to trap impurities in water, not gasses...using one is guaranteed to block your vent line. Modifications to the tank vent to allow more oxygen exchange and the use of K.O. or Odorlos according to directions will eliminate odor out the vent for a LOT less than the cost of just one filter and is a lot easier to maintain.
I wish I could put a product on the market that creates the very problem it's sold to solve...that's what a holding tank vent filter does. Oxygen is the key to odor elimination...when organic matter breaks down aerobically (oxygenated), it doesn't stink...it's only when it breaks down anaerobically (without oxygen) that it can create noxious hydrogen sulfide gasses. A filter traps those gasses, but it also prevents any exchange of air through the vent line, causing the tank to become anaerobic/stinky. So not only do they create the problem they're sold to solve, but they're also VERY expensive. They only last a year at most...are toast immediately if they get wet--which is almost impossible to prevent on most sailboats, because even a half-full tank spills into the vent line when the boat is heeled. And when the charcoal gets wet it swells, creating a blockage that leads to a pressurized tank and the disasters THAT can cause. Icemaker water line filters are designed to trap impurities in water, not gasses...using one is guaranteed to block your vent line. Modifications to the tank vent to allow more oxygen exchange and the use of K.O. or Odorlos according to directions will eliminate odor out the vent for a LOT less than the cost of just one filter and is a lot easier to maintain.
Peggy I may have accidently solved some
of the problems that I have been read about in this thread. When I built the system for Bietzpadlin I relied on my knowledge of plumbing because I had no knowledge of the holding tank set-ups on boats. I built a fiberglass tank that fits in the bilge. The waste pipe and the vent are located on the forward end of the tank at the top. The waste line extends into the tank to the lower aft end and is cut out on the sides of the exit end to allow waste to flow either right or left. This same line serves as the pump out line by way of the Wye valve. The vent line runs forward and up to the main bulkhead to a point just below a cowl vent and terminates in a painters respirator cartridge. Every time the head is flushed air is pumped into the bottom of the accumulated waste and vented through the cartridge. I placed a surge tank in the vent line to preclude the chance of liquid over topping the outlet of the vent. The system was assembled in 1999 and has been in use ever since. I pump the tank when it is full or when we plan to go out for a few days. I think that discharging the waste into the bottom of the tank along with the air from the drying mode helps to aerate the load of waste and avoid anaerobic decay. This is just my experience and observations. Ross
of the problems that I have been read about in this thread. When I built the system for Bietzpadlin I relied on my knowledge of plumbing because I had no knowledge of the holding tank set-ups on boats. I built a fiberglass tank that fits in the bilge. The waste pipe and the vent are located on the forward end of the tank at the top. The waste line extends into the tank to the lower aft end and is cut out on the sides of the exit end to allow waste to flow either right or left. This same line serves as the pump out line by way of the Wye valve. The vent line runs forward and up to the main bulkhead to a point just below a cowl vent and terminates in a painters respirator cartridge. Every time the head is flushed air is pumped into the bottom of the accumulated waste and vented through the cartridge. I placed a surge tank in the vent line to preclude the chance of liquid over topping the outlet of the vent. The system was assembled in 1999 and has been in use ever since. I pump the tank when it is full or when we plan to go out for a few days. I think that discharging the waste into the bottom of the tank along with the air from the drying mode helps to aerate the load of waste and avoid anaerobic decay. This is just my experience and observations. Ross
A couple of questions, Ross...
Boat sanitation plumbing doesn't have a whole lot in common with plumbing in buildings...a couple of things I THINK you said worry me a bit... Your line from the toilet to the tank and the tank discharge/pumpout line are the same line, going into the same fitting? Your tank vent line terminates in a respirator cartridge INSIDE the boat? If the answer to both those questions is yes, your system may be working ok--by your standards--but it violates at least one CG regulation and has the potential to create far more problems than you think it solves. Because methane is flammable, and because the gasses--hydrogen sulfide and sulfur dioxide--generated by waste breakdown in an anaerobic environment are highly toxic, even lethal in high enough concentration, CG regs (Title 46) require that all waste tank vents terminate in a fitting on the outside of the boat. Terminating in a respirator cannister inside a cowl doesn't meet that requirement. Your tank can't help but be anaerobic...its location, length of the vent line, the addition of a "surge tank" AND the cannister make impossible for the tank to breathe at all. Flushing the toilet doesn't aerate the contents, it just stirs 'em up. Aeration requires a continuous supply of air 24/7. If you don't think your tank is anaerobic, remove the cannister (which you'd have to do to pass a CG inspection) and flush the toilet. But when the inlet is at the bottom of the tank, most toilets can't overcome the backpressure created by weight of the contents...making a backup a very real risk. That your tank is below the toilet minimizes that risk, but doesn't eliminate it if the vent ever becomes clogged, causing the tank to become pressurized. You installed it in 1999, so you've obviously gotten away with it--at least so far...but it's not a design that ANYONE else should copy....'cuz it doesn't meet any marine standards.
Boat sanitation plumbing doesn't have a whole lot in common with plumbing in buildings...a couple of things I THINK you said worry me a bit... Your line from the toilet to the tank and the tank discharge/pumpout line are the same line, going into the same fitting? Your tank vent line terminates in a respirator cartridge INSIDE the boat? If the answer to both those questions is yes, your system may be working ok--by your standards--but it violates at least one CG regulation and has the potential to create far more problems than you think it solves. Because methane is flammable, and because the gasses--hydrogen sulfide and sulfur dioxide--generated by waste breakdown in an anaerobic environment are highly toxic, even lethal in high enough concentration, CG regs (Title 46) require that all waste tank vents terminate in a fitting on the outside of the boat. Terminating in a respirator cannister inside a cowl doesn't meet that requirement. Your tank can't help but be anaerobic...its location, length of the vent line, the addition of a "surge tank" AND the cannister make impossible for the tank to breathe at all. Flushing the toilet doesn't aerate the contents, it just stirs 'em up. Aeration requires a continuous supply of air 24/7. If you don't think your tank is anaerobic, remove the cannister (which you'd have to do to pass a CG inspection) and flush the toilet. But when the inlet is at the bottom of the tank, most toilets can't overcome the backpressure created by weight of the contents...making a backup a very real risk. That your tank is below the toilet minimizes that risk, but doesn't eliminate it if the vent ever becomes clogged, causing the tank to become pressurized. You installed it in 1999, so you've obviously gotten away with it--at least so far...but it's not a design that ANYONE else should copy....'cuz it doesn't meet any marine standards.
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