auto vent use

Toilets do not require a vent. They are a full siphoning fixture and get all the vent they need from the air above the bowl

Yes, thanks for your input, I will remember the shop vac trick, and one point to add: I have a 1 1/2" AAV above the sink trap and one that comes up alongside of the toilet tank and is a little higher than it. I am trying to determine if I have at least a satisfactory arrangement or if something is radically wrong. I don't know if you could read through one of the earlier posts which describes the layout. Thanks Also, should I just take off the AAV at the sink, put a 90 on it and run it horizontally through the cabinet, behind the tank and T connect it to that vent pipe the toilet AAV is currently connected to, and run a pipe on out the roof? This is my big question. This air trap thing has happened in the past, no obstructions, but I continued to add parts to a vent system and Maybe I'm good as it is - that is what I have been asking.
Because it has been inconsistent in the past, is being inconsistent now, but now it is working or at least today it did. Thanks

Tom, thanks for hanging in here on this, you have maintained there is an obstruction, but I assure you there is not and that is why I hope to find out if there is something wrong with the alignment as I have described it preventing as one guy said, "the air being evacuated before the water." Maybe I should just let time tell if there is a continued problem, but it is inconvenient when it stops up when I think it should work. That is why I am asking about the alignment of the pipes and relationship with the AAVs. Believe it or not, this is giving me a lot of understanding and things to consider for future projects.

air

ANYTHING in the line which obstructs it, whether water or a mass, if it is between the fixture and a standard vent out the roof, will prevent drainage, because water can only enter a pipe, it the same amount of air can escape from it. An AAV will let air in to prevent siphonage, but it CANNOT let air out to prevent improper drainage.

HJ, I'm capitalizing your initials because I think you are onto something. That point about siphonage vs drainage is everything. Let me see if I am guessing at this right. The AAV allows just enough air to enter the system so the trap does not get siphoned, but possibly not enough air to create pressure to provide drainage.
So, should I convert the AAV system to an open air through the roof vent? Or go with a larger AAV? There are no other obstructions up or down the drain line when there have been stoppages in the past. Thanks!

An AAV is a ONE-WAY valve, if it were to let air out, you'd get sewer gas out, and is one reason why they are not liked well...they DO eventually leak, and need to be replaced. An atmospheric vent normally never needs service. Now, that doesn't mean a bird, or squirrel or something might clog it, but that's not normal, nor need replacement, just clearing.

The size of the AAV has nothing to do with it.

The toilet outlet is normally no bigger than a little over 2" - the pipe you are trying to dump it into is normally at least 3", the only reason it can't move air in front of the dump is THERE'S SOMETHING BLOCKING IT! it's not air.

It's hard to tell sometimes if a toilet is plugged internally. Depending on the shape of the internal trap, you may not see it from either the top OR the bottom. Sometimes in these cases, a good toilet auger will catch it and remove it, but not always.

Worse comes to worse, take the thing out, take it outside, set it on a bucket or something sturdy that would allow it to flush. Dump some toilet paper into it, then flush and see if it all comes out well. It might take a couple of times, or a varying amount of TP, but odds are, there's something caught inside the trapway of the toilet. Unless the line is already plugged and there's no place for the waste to go, when you flush a toilet, and it doesn't go anywhere, it's almost always the toilet and not a vent problem...a toilet will flush fine without a vent.

OK, Jadnashua, I hear you, but what happened when it would not flush and I looked up and down the clean out and the drain line was open both ways, and I even ran a hose from the clean out that flowed into the septic tank which I could observe, and then when I removed the AAV by the tank, and it drained instantly? This was repeated several times. And even, I remember now, water would splash up from the sink. That also repeated several times. I think at the time I got a new AAV. I know it sounds bizarre, but that's what I/we observed. That is why I suspected venting as a problem. At one point I did remove the toilet and thoroughly inspected it, though I never flushed it as you suggested. Have fun and thanks. I'm learning a lot.

What is the make and model of the toilet?

American Standard 6.0 1.6 g/flush

Tom Sawyer said:

Toilets do not require a vent. They are a full siphoning fixture and get all the vent they need from the air above the bowl

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So tell that to he inspector. I don't believe it .... toilets move the most water the fastest, and need air after the trapway to do so.

ballvalve said:

So tell that to he inspector. I don't believe it .... toilets move the most water the fastest, and need air after the trapway to do so.

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Thanks everyone for the discussion. I have decided to take the auto vent off by the toilet tank and run the pipe on out the roof; it sounds right that what might be missing is air pressure (I don't know if this is the right language)to help release the water. Mentioning siphonage versus drainage was something that had not been considered. It was flushing fine when I left today. thanks again for all of your time.

Thanks everyone for this discussion. I decided to remove the AAV at the toilet tank and extend the pipe on out through the roof. The point about an AAV providing anti-siphonage assistance but not air pressure to assist drainage made sense. It is still a puzzle, though, because every thing I checked indicated that the AAV was installed correctly and should have been effective for the a toilet application which I would assume means - it should drain. I don't just want anti-siphonage, I want DRAINAGE. Still a little confused, but I think this is the right approach. Thanks again to everyone and for your time. Happy plumbing! A truer oxymoron there could not be.

Since it is not uncommon for the need for air to move BOTH ways, on a dedicated line, only using an AAV can cause problems. You can't use only an AAV on a line, somewhere, it has to have a path to the atmosphere. IOW, you couldn't build a house while only using AAVs, you'd need at least one tie-in to an atmospheric vent. The AAV is desinged to prevent siphoning a trap, but it cannot provide air exchange to allow waste to flow against an air column. Normally, the pipe doesn't fill, and air can still move, but...

ballvalve said:

So tell that to he inspector. I don't believe it .... toilets move the most water the fastest, and need air after the trapway to do so.

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The IPC no longer required a separate vent for a toilet and in fact lists the vent to fixture distance as "unlimited" that is because a toilet (and all fixtures for that matter) get plenty of air from the atmosphere pushing down on the drain. In fact, no fixture needs a vent to drain. sinks, toilets etc will all drain just fine with no vent at all and in fact a lot of them will drain too well without a vent which causes the trap to siphon. Vents are not there to help drain fixtures, they are there to prevent traps from siphoning bu equalizing the pressure or vacuum in the system. Toilets are full siphoning fixtures designed to completely evacuate all of the contents of the bowl and its trap way. The trap then is refilled by the toilet fill valve. The addition of or removal of the AAV in this case has nothing at all to do with the proper operation of the toilet. If removing the AAV lets the toilet drain it is only because there is something downstream that is preventing the discharge from freely flowing to the sewer or septic tank so...there are two possibilities left. One is that the septic tank is full (most likely) and two is that the toilets jet is plugged, common with American Std toilets and the reason I asked what type of toilet he has.

Tom, I like your report and solid information, it is helpful for furthering understanding. The final diagnosis though can't be accurate. When the breaks would come and the water would flow, I could see it entering the septic tank. I would stuff the toilet with paper towels and flush it and run out to see it fall into the septic. That was after thoroughly snaking the line from the cleanout to the septic, and then eventually it would lock up again and that is like you said when I would pull the AAV and flushing would occur - there were no obstructions. The last point you made about Am St toilets' jets plugging is something I never heard of and didn't know could happen. The only thing about that is that it was a very new toilet, not used very much because it is in a remote part of the house, and the third option for toilets in the house - so can new toilets have plugged jets and what do you do with plugged jets or how do you diagnose it for sure? thanks for your help.

Any toilet could have a defect in it from the factory. Some brands have fewer than others. AS from a big box store tends to have more defects than even the same toilet sold at a plumbing supply house. Rumor has it one way the big box stores get the price is the manufacturer gets to bypass some QA/QC checks...essentially letting the buying customer be the one to decide if it is perfect or not.

Something dropped in the toilet or the tank that got caught in the siphon jet, slowing or restricting the flow, can prevent the initial flush action from occuring. Some toilet flappers come with little floats designed to help the flapper close at the proper time - plumbers have sometimes reported finding more than one caught in the path from the tank to the bowl after they came loose from the flapper.

Something caught in the trapway might flush an all liquid dump perfectly fine, then get some paper or solid waste to catch on the clog (common ones are pencil, cotton swab, feminine product, comb, bobby pin, small toy, etc.), and things slow down or stop.

If the pipe is full for some reason downstream of the toilet, it won't flush, either.

have you opened the septic tank lid at inlet end to see if by chance the baffle is broken off, or plugged, not allowing the air to be "pushed" ahead of the water...
if you want to directly test if it's the AAV,,, when the toilet plugs , let it fill up, now while still full remove the AAV... if the water flushes away then you know it was the AAV causing the problem.
every system needs an opening to open air, and AAV's should not be used where they are subject to backpressure...
finally, a toilet wil flush without a vent, as long as the water can move.... take any toilet and set it on a bucket, wood frame, etc.....fill tank with water, flush, and watch water come out the bottom.....

I checked out a new toilet that wouldnt flush. Half the rim jets were clogged.
At another house the water level was not high enough. First solid use backed it right up.

It's a bit confusing of your problem and I think your saying that the toilet doesn't flush every time and at times it will. Do you hear any gurgling from the sink drain when the toilet is flushed? My experience is; My brother-in-law finished off a basement apartment and had a "friend" do the plumbing. The problem was he used an AAV that could not handle the air volume needed for the toilet. It would hardly flush and when the AAV was removed every thing worked OK. You could actually hear the air getting sucked in the the air vent pipe with the AAV removed. There are different size AAV's. Go to http://www.oatey.com/Channel/Home.html for info. Maybe at times the main drain is getting enough air by pulling it from the other AAV but you would think the problem should occur every time, however, mikeplummer suggestions seems more plausible.

mikeplummer said:

have you opened the septic tank lid at inlet end to see if by chance the baffle is broken off, or plugged, not allowing the air to be "pushed" ahead of the water...
if you want to directly test if it's the AAV,,, when the toilet plugs , let it fill up, now while still full remove the AAV... if the water flushes away then you know it was the AAV causing the problem.
every system needs an opening to open air, and AAV's should not be used where they are subject to backpressure...
finally, a toilet wil flush without a vent, as long as the water can move.... take any toilet and set it on a bucket, wood frame, etc.....fill tank with water, flush, and watch water come out the bottom.....

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Mike; You have said it once and I have said it three times here but nobody seems to understand. I'm betting that if the main line here is clear and has no sags, then either the toilet is defective which is real common with American Std toilets or as you said, there is something in the septic tank that is not allowing water to flow. Either a broken pr plugged baffle or a full tank