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Old 06-13-2010, 11:42 PM   #1
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Air admittance vent with septic system.


I have a cabin in a remote area that is off the grid. Building code is not an issue.
I have a septic system made from two 55-gal drums. When I installed a toilet and sink, I installed an air inlet valve under the sink, to provide venting for the waste line. I did not want to vent through the roof.
When I flush the toilet, the water in the bowl swirls around but does not go down the drain. When I remove the air inlet vent and just leave the pipe stack open, the toilet works.
I read in the instructions that came with my Oatey Sure-Vent valve that if it is used with a septic system, the 1st stage of the septic system should be vented to the atmosphere. Is this to allow air to escape from the septic tank when waste water enters? Is this why my toilet will not flush?
Is there back pressure that will not allow the water to go down the waste pipe? If not, what could be causing this problem?
Please don't lecture me about building codes. I just want to know why the toilet will not flush.
See attached drawing.
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Attached Thumbnails
Air admittance vent with septic system.-septic-skech.jpg  
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Old 06-14-2010, 01:39 AM   #2
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Air admittance vent with septic system.


The toilet won't flush unless you vent the toilet drain. If you don't won't to vent through the roof, go through the crawlspace wall from a T above the sink drain connection and up to under the eave overhang on the outside wall. The wind will probably carry away the methane gas from the system.
Good luck!
Mike
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Old 06-14-2010, 07:12 AM   #3
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Air admittance vent with septic system.


What you have is basically a totally sealed sewer/septic system. Since you have no actual open vent to atmosphere, you are not allowing air to escape the line when the toilet is flushed. Your system is trying to jam water down an air sealed pipe. Your AAV valve will allow air to enter the system, but there is no way for air to get out of the system ahead of the water flow. You either need to entend the sink drain to atmosphere (this will act as a wet vent to the toilet), or vent the first 55 gallon drum above ground. I would recommend extending the sink drain as a vent through the roof or somewhere outside instead of venting the drum, the smell from the drum will be more noticable from ground level vs venting above the structure.
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Old 06-14-2010, 08:40 AM   #4
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Air admittance vent with septic system.


You seem to be comfirming my theory. Does the toilet flush with the vent valve off because the septic tank air can go up and out and "pass" the water as it goes down since the 4" pipe is not completely full of water when it flushes? Is that what a "wet vent" is ?
I cannot vent through the roof because it is too steep to climb on, I don't have an attic (it is vaulted), and the roof is metal (I don't want to mess it up). I do have a flapper vent on the outside wall above the toilet because I thought I was going to put in a vent fan. I may just use that opening and run the vent up the outside wall (vinyl siding). Can it go up to under the roof eave, which would be about 2-3 feet above the highest window, or does it have to be above the roof? I have a roof brow that I would have to "go around" if I need to go above the roof. Again, not a code question, just a functionality question. I would think that if the septic gases are lighter than air, they would rise out of the vent pipe and go up around the brow/eave.
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Last edited by Roy Rowlett; 06-14-2010 at 08:57 AM.
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Old 06-14-2010, 09:53 AM   #5
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Air admittance vent with septic system.


Quote:
Originally Posted by Roy Rowlett View Post
You seem to be comfirming my theory. Does the toilet flush with the vent valve off because the septic tank air can go up and out and "pass" the water as it goes down since the 4" pipe is not completely full of water when it flushes? Is that what a "wet vent" is ?
I cannot vent through the roof because it is too steep to climb on, I don't have an attic (it is vaulted), and the roof is metal (I don't want to mess it up). I do have a flapper vent on the outside wall above the toilet because I thought I was going to put in a vent fan. I may just use that opening and run the vent up the outside wall (vinyl siding). Can it go up to under the roof eave, which would be about 2-3 feet above the highest window, or does it have to be above the roof? I have a roof brow that I would have to "go around" if I need to go above the roof. Again, not a code question, just a functionality question. I would think that if the septic gases are lighter than air, they would rise out of the vent pipe and go up around the brow/eave.
Thanks
With the valve off, the air is pushed up the sink drain line and out the exposed pipe when the toilet is flushed. the air must be displaced somewhere so the water can enter the system.
A wet vent is a single pipe that performs two functions. It drains the water out of the sink when the sink is in use, and also performs as the vent line for an adjacent fixture, most likely a toilet, but sometimes a shower or bathtub can be wet vented through the sink drain..
The vent "should" go above the roof, but since your system is not bound by any codes, you can vent out the side wall. Your "supposed" to maintain a minimum distance from any operable windows and doors to prevent sewer gas from coming back in your house, so if you can pipe it along the wall away from any windows before you terminate it below the roof edge, you'll make your system functional again.
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