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Old 07-16-2011, 01:32 PM   #1
ctchas
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Default New Toilet makes shower drain gurgle

Looking for advice for venting problem. Since this is my 1st post I'm not sure if I can attach a picture for viewing. Hopefully my description will suffice if I can't.
Everything down there is PVC.
Vent through roof and toilet drain is clear. No flushing or draining problems with toilet or shower or anywhere in house. Toilet flushing causing gurbling sounds in shower drain and over time empties the shower trap.
Shower drain (2") connection is directly below the toilet flange connection then drainage drops down to 3" elbow. Approx 30" downstream of the elbow there's a wye connection which is a vent going up through the roof.
After doing some research I see where the "critical distance" for the fixture/vent should be 5 ft maximum. House is about 22 years old and the shower does not have a separate vent so I'm guessing Mr. Inspector might have missed this one.
The old low flow toilet worked just fine and never cause gurgling or trap emptying characteristics.
I'm not real excited or interested in installing an AAV (if permissible) since it's down in the crawlspace and I'd like to do the job without ever having to visit the area again.
I'm considering installing a wye in the 2" shower drain approximately 2 ft after the trap, rolled up at least 45 degrees (outlet of wye facing trap?). I'll need to use a 90 elbow go through 1 joist, another 90 and I'd probably have maybe 4 feet of 1 1/2" pipe running horizontally then go up (another 90) through a wall and connect it in the attic before it goes through the roof.
Any problems with the horizontal vent run? Regular 90's OK? Any other issues I should be concerned with?



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Old 07-16-2011, 02:23 PM   #2
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The distance of the horizontal vent wouldn't cause this problem. Also, 22 years ago, the rules were not nearly as involved as today, so this may have been acceptable.

Anyway, since the problem started when you changed toilets, what change did you make? Did you install another low-flow? At any rate, if you didn't have the problem before and you have it now, it is because the toilet is putting water into the line at a faster rate...it can be the same amount, but just a faster rate. This is causing the gurgle and siphon. The problem isn't so much the shower drain as it is the point of connection to the stack. Since it is below the toilet connection, you have this problem.

Check the stack vent first. Is it 3" or 4" all the way up? Also, make sure the stack is not blocked. It could have leaves, dirt, or a dead bird in there!

I wouldn't bother with the venting of the shower as you described, as the problem is the connection. If you're allowed, you could do an internal vent, though most places don't allow them anymore.

If the vent is clear, the next option would be to see whether you can install a 'branch vent' (I use the term loosely here) and tee off the shower drain to make a second connection above the connection to the toilet.

Hope this helps.



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Old 07-16-2011, 05:17 PM   #3
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Thanks for your input.

The old toilet was the old 3+ gallon style. New one is an American Standard Cadet 3.

Stack drain is 3" all the way up and clean as a whistle.

A little puzzled that you mentioned "I wouldn't bother with the venting of the shower as you described, as the problem is the connection", yet at the end of your reply you say "If the vent is clear, the next option would be to see whether you can install a 'branch vent' (I use the term loosely here) and tee off the shower drain to make a second connection above the connection to the toilet".

There is no place right above the toilet as the vent is downstream.

Isn't this "branch vent" you're suggesting the same as what I was suggesting in my original message? Obviously I don't want to get involved with changing the original vent stack location. Wouldn't a new vent on the shower line remove the threat of sucking the shower trap dry.

Thanks again

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Old 07-16-2011, 09:53 PM   #4
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I understand that you stated that there were no drainage problems, but just to make me happy, give the toilet at least 6 consecutive flushes while having all cold water in the house running at every fixture for about 5 minutes.

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Old 07-16-2011, 10:11 PM   #5
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I think I understand what is happening.
You said the 2" line is directly below the toilet flange. This is improperly connected.
The shower does not have a vent.
When you flush the water going down the 3" past the 2" shower drain actually sucks the water out of the shower p-trap.
The newer toilets are more efficient and even though it is a low flow the water being flush passes through the toilet much faster and the volume sucks out the shower trap.

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Old 07-16-2011, 11:18 PM   #6
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Default Re: Caduceus

Got a couple of people to stand by sinks & drains and even had them flush the other toilet on the other end of the house a few times during the process. Did the toilet (in question) flush 8 times (added two just for laughs and giggles.

I'd like to add this is a one story home.

No problem with the drainage but certainly had a lot of shower drain noise by the eighth flush. Filled the trap again after I finished just to be safe.

I'm still thinking if I cut a vent in the shower drain it'll solve the problem.

If anyone agrees - is there any reason my suggested pipe run for the added vent wouldn't meet code requirements. I have a Pipefitting background but know little about the Plumbing Codes. Give me a Main Steam project and there'll be no questions asked. I know when to ask for help.

Thanks all for your comments.

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Old 07-17-2011, 12:05 AM   #7
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I think Mr. David (as is usual), quite possibly has the best solution. If you can cut in a tee onto the vent stack and run straight to the shower drain from that, your problem should be solved. How far is it in a straight line from the vent stack to the shower drain?

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Old 07-17-2011, 12:56 AM   #8
ctchas
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Default Re: phishfood/mr. david

The distance is approximately 8 feet. Also very little room to add additional fittings in that area.

I'd like to ask again. If I add a vent to the shower drain - wouldn't that correct the syphoning action on the shower trap?

Thanks for the suggestions.

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Old 07-17-2011, 01:11 AM   #9
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It sounds as though it would fix the gurgling problem.

The reason we are looking for you to tie into the vent stack is three fold.

First, it is much easier. There is no need to cut into walls to add vent stacks, go up in the attic to revent, drill through joists and wall plates, etc.

Second, you mention having to pass through joists with the vents. Every time you drill through a load bearing joist, you weaken it. You don't want to create a structural problem while fixing a plumbing problem.

And then there is the issue of a flat vent. Most codes disallow a vent that runs horizontal until the vent pipe is well above the fixture that it vents, so that the vent will not become clogged with solids if the drain backs up. It sounds as though you are considering running the vent horizontal underneath the floor, which obviously violates that provision of the code.

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Old 07-17-2011, 01:21 AM   #10
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I appreciate your info.

I'll look into your suggestion.

If I do decide to run the vent I'll go through the middle of a joist and support it top and bottom of hole. I believe I'll be able to run the piping uphill an inch or two in a 3 or 4ft span.

Thanks again.



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