Peggy, I am installing a holding tank in my sailboat and would like to know how to locate where to install the tank vent. The easiest location is on the port hull near the tank. However, when the boat is heeling the vent will be below the waterline. Can I install a scupper valve, or do I need to run a line aft? If so, how far can I run a vent hose? The longer the hose run, the harder it is to avoid low points. Also, as you advise in your book, I am installing a vented loop in the seawater inlet between the pump and the bowl. Can I tie the vent hose from the top of the loop to the holding tank vent? This would save me from adding an additional thru hull, but I am concerned that odor from the tank my find its way to the bowl. Speaking or thru hulls for the holding tank vent, do you recommend just an ordinary mushroom type like I might use for a sink drain? Thanks for your help. VR, Dave (P.S. You book is great! You hit on all the right stuff.)
Holding Tank Vent Installation Questions
- Thread starter Dave Bennett
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Where will the tank be located in the boat?
Where to run the vent line depends on the tank location...if it's under the v-berth, run it forward off the top at the bow end, inboard side of the tank to a thru-hull (open bulkhead is fine) in the hull about a foot below the toe rail. That far forward, the vent thru-hull won't be in the water even if your rails are. If the tank will be further aft, I need to know where before I can tell you where to run the vent. If the air valve in the vented loop is working properly you shouldn't need a vent line off it...'cuz the air valve only allows air INTO the line, nothing out. Plus, the diameter of any vent line off a vented loop is so small (1/4") that any waste squirting out of it will clog it up very quickly...which renders it useless as a siphon break. You might as well just have a unvented loop in the line. Btw...there aren't any "no discharge" waters--at least none of any size--within at least a couple hundred miles of you...which means the discharge of treated waste is legal. Have you considered installing a Lectra/San (Type I MSD that treats a flush at a time and discharges it legally) instead of a new tank? No odor, less plumbing, no vent required, so no new holes in your boat, doesn't use any chemicals, and is the most environmentally friendly solution to onboard waste around. The $700+ average price can seem a bit staggering...till you weigh it against how much a new tank and all the related "stuff" is gonna cost you...and then figure in the annual cost of pumpouts and tank products. A Lectra/San will pay for itself in just couple of years. Why carry around waste if you don't have to???
Where to run the vent line depends on the tank location...if it's under the v-berth, run it forward off the top at the bow end, inboard side of the tank to a thru-hull (open bulkhead is fine) in the hull about a foot below the toe rail. That far forward, the vent thru-hull won't be in the water even if your rails are. If the tank will be further aft, I need to know where before I can tell you where to run the vent. If the air valve in the vented loop is working properly you shouldn't need a vent line off it...'cuz the air valve only allows air INTO the line, nothing out. Plus, the diameter of any vent line off a vented loop is so small (1/4") that any waste squirting out of it will clog it up very quickly...which renders it useless as a siphon break. You might as well just have a unvented loop in the line. Btw...there aren't any "no discharge" waters--at least none of any size--within at least a couple hundred miles of you...which means the discharge of treated waste is legal. Have you considered installing a Lectra/San (Type I MSD that treats a flush at a time and discharges it legally) instead of a new tank? No odor, less plumbing, no vent required, so no new holes in your boat, doesn't use any chemicals, and is the most environmentally friendly solution to onboard waste around. The $700+ average price can seem a bit staggering...till you weigh it against how much a new tank and all the related "stuff" is gonna cost you...and then figure in the annual cost of pumpouts and tank products. A Lectra/San will pay for itself in just couple of years. Why carry around waste if you don't have to???
Holding Tank Vent Installation and Tank Location
Thanks for your response. The tank is right in the middle of the boat, just aft of the mast and port of centerline. The rail amidships will go in the water in a stiff wind, so I will probably run the vent line aft. I am concerned that I will not be able to avoid low points on a long (20 ft) run to the transom. For a 20 ft run, should I still use 5/8” ID hose with a 5/8” mushroom through hull? If I run it outboard just forward of the cockpit, I can be above the waterline in a heel, but will this odor waft into the cockpit? As far as the Lectra/San is concerned, I am concerned that my electrical system is not robust enough to handle the power demand. If my family spends a long weekend on the boat, we may not have enough electricity for the Lectra/San, lights, and engine starting capacity. I have not generators onboard. I prefer having a manual system independent of any electrical requirements.
Thanks for your response. The tank is right in the middle of the boat, just aft of the mast and port of centerline. The rail amidships will go in the water in a stiff wind, so I will probably run the vent line aft. I am concerned that I will not be able to avoid low points on a long (20 ft) run to the transom. For a 20 ft run, should I still use 5/8” ID hose with a 5/8” mushroom through hull? If I run it outboard just forward of the cockpit, I can be above the waterline in a heel, but will this odor waft into the cockpit? As far as the Lectra/San is concerned, I am concerned that my electrical system is not robust enough to handle the power demand. If my family spends a long weekend on the boat, we may not have enough electricity for the Lectra/San, lights, and engine starting capacity. I have not generators onboard. I prefer having a manual system independent of any electrical requirements.
Don't run it aft...
You want the shortest straightest vent line possible. Go forward to just below the toe rail and put a clam shell cover over it to keep water out. And go with a 1" vent regardless of length. Or better yet, let's find a better location for the tank...where's the head located in the boat? As for the power demands of the Lectra/San...1.7 AH/flush seems a little scary...till you compute actual total usage. The average adult only uses the head a maximum of 5x/day, so a family of 4 will only consume a max of 35A/day (and a lot of people don't run it for it urine only--illegal, but no harm to the environment). That's not a lot of power consumption, even over a 3 day weekend. And besides, other demands make it just about impossible for most people to go 3 days without running the engine even once to recharge batteries, even without a Lectra/San...so power consumption isn't nearly as much of an issue for most sailboat owners as they think it is unless their power resources are very marginal. But...up to you whether to deal with maintaining a holding tank with all its vent and odor issues, pumpouts etc or have the convenience of being able to flush it and forget it. To each his own.
You want the shortest straightest vent line possible. Go forward to just below the toe rail and put a clam shell cover over it to keep water out. And go with a 1" vent regardless of length. Or better yet, let's find a better location for the tank...where's the head located in the boat? As for the power demands of the Lectra/San...1.7 AH/flush seems a little scary...till you compute actual total usage. The average adult only uses the head a maximum of 5x/day, so a family of 4 will only consume a max of 35A/day (and a lot of people don't run it for it urine only--illegal, but no harm to the environment). That's not a lot of power consumption, even over a 3 day weekend. And besides, other demands make it just about impossible for most people to go 3 days without running the engine even once to recharge batteries, even without a Lectra/San...so power consumption isn't nearly as much of an issue for most sailboat owners as they think it is unless their power resources are very marginal. But...up to you whether to deal with maintaining a holding tank with all its vent and odor issues, pumpouts etc or have the convenience of being able to flush it and forget it. To each his own.
Questions on the Lectra/San
Is it legal to use these devices in rivers (Mississippi or Illinois) or in an inland lake such as where I am located now (Carlyle Lake). Thanks Peggy. I love to read your Posts! Dan B. 1972 C-27 "Sotto voce"
Is it legal to use these devices in rivers (Mississippi or Illinois) or in an inland lake such as where I am located now (Carlyle Lake). Thanks Peggy. I love to read your Posts! Dan B. 1972 C-27 "Sotto voce"
The Lectra/San is legal on most rivers
that are "navigable interstate waterways" (capable of navigation by interstate vessel traffic). However, ALL "non-navigable" waters (freshwater lakes, freshwater reservoirs or other freshwater impoundments whose inlets or outlets are such as to prevent the ingress or egress by vessel traffic subject to this regulation, or in rivers not capable of navigation by interstate vessel traffic") are "no discharge" waters...you would not be able to use a Lectra/San on them. Which means you can use one on almost all of the Mississippi and Illinois Rivers...but whether you can on Carlyle Lake depends on whether it's a part of the river that's a municipal water supply or a non-navigable lake that isn't part of either river.
that are "navigable interstate waterways" (capable of navigation by interstate vessel traffic). However, ALL "non-navigable" waters (freshwater lakes, freshwater reservoirs or other freshwater impoundments whose inlets or outlets are such as to prevent the ingress or egress by vessel traffic subject to this regulation, or in rivers not capable of navigation by interstate vessel traffic") are "no discharge" waters...you would not be able to use a Lectra/San on them. Which means you can use one on almost all of the Mississippi and Illinois Rivers...but whether you can on Carlyle Lake depends on whether it's a part of the river that's a municipal water supply or a non-navigable lake that isn't part of either river.
Marine Head Installation
Link below shows marine head install on a Cape Dory 25. (click View Album, then Chapter 3)Vent and deck discharge on port side. Difficult install because of space limitations. Mascerator is mounted under holding tank support board. Have never used it as we get a pumpout service with the hull cleaning but did work great when first installed with all fresh water. I believe you have to be offshore over 3 miles to actually use the hull discharge system. Hope this helps.
Link below shows marine head install on a Cape Dory 25. (click View Album, then Chapter 3)Vent and deck discharge on port side. Difficult install because of space limitations. Mascerator is mounted under holding tank support board. Have never used it as we get a pumpout service with the hull cleaning but did work great when first installed with all fresh water. I believe you have to be offshore over 3 miles to actually use the hull discharge system. Hope this helps.
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