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Thread: Tub drain Venting

  1. #1
    DIY Junior Member mrbeing123's Avatar
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    Default Tub drain Venting

    OK. I have a late 1800's I moved that was gutted. I am almost done with the bathroom/laundry room except for plumbing the tub drain and vent. Please see attached pictures. What would be the best or correct way of plumbing this. I am sure it is fairly simple but at the same time I can't find anything on line or in books of doing it this way. Can you vent the tub before the tub drains into the drain line? Both walls that the tub touch are exterior. If possible I would like to run the vent on the exterior of the wall. Under Louisiana plumbing code. I am aiming for minimal vertical height with this as I have barely enough vertical clearance to maintain the drain line slope and clear a girder that I must pass over before reaching the main line

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    Last edited by mrbeing123; 12-06-2012 at 08:14 AM.

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    The vent comes off the top of the trap arm. This is what breaks the siphon.

    If the vent comes off lower then the trap, it will siphon.

    One of those is shaped like an S, that is a "No go". Can't do that.

    You need at least three vents there.
    The tub, the lav and the washer. These need vents.
    If the lav were closer, you could wet vent the lav and the toilet together. So really, you're looking at four vents there.
    When you pull the permit and the inspector comes out, he can verify the job.

    There was a while there, where I was getting a plumbing inspection every day. I ran a three man crew and we plumbed five "3-bath" homes a week. Those were splits with a lower floor groundwork. You can't do them that fast if you have a crawl on the first floor.
    Last edited by Terry; 12-06-2012 at 08:49 AM.

  3. #3
    DIY Junior Member mrbeing123's Avatar
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    Thank for replying. The lav and the washer are vented each individually and reconnect to main 3" vent in attic. The toilet is vented through the main vent which is close enough for 3" pipe. I know my drawing is terrible, but just to clarify if I understand what you said.. Assuming I make the trap arm at least 2x pipe diameter and therefore no s-traps and each fixture is vented independently, will either of these configurations work to properly vent the tub? or just the top configuration?
    Last edited by mrbeing123; 12-06-2012 at 09:09 AM.

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    This one.
    Notice that the vent comes off the "top" of the trap arm?
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  5. #5
    DIY Junior Member mrbeing123's Avatar
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    Thanks Terry, I now understand what you said. Makes a lot of sense now. Haha yes. lots of open crawls here on old and new houses. Makes for fun work in the rain.

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    Moderator & Master Plumber hj's Avatar
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    quote; Assuming I make the trap arm at least 2x pipe diameter and therefore no s-traps

    An "S" trap has NOTHING do with the "2x pipe diameter" or anything else EXCEPT how it is configured. You can have a "S" trap with 10 x the pipe diameter.
    Licensed residential and commercial plumber

  7. #7
    DIY Junior Member mrbeing123's Avatar
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    Quote Originally Posted by hj View Post
    quote; Assuming I make the trap arm at least 2x pipe diameter and therefore no s-traps

    An "S" trap has NOTHING do with the "2x pipe diameter" or anything else EXCEPT how it is configured. You can have a "S" trap with 10 x the pipe diameter.
    I am using the descriptions all my references and code book says. I understand it's a bit more complicated than just making it 2x the pipe diameter. Though my education is mechanical engineering, fluid statics, dynamics, and kinematics were all part of the program but I really fought it tooth and nail. I am trying to imagine an s trap with the tee entrance 10x the pipe diameter from the wier. I think it would be a great material for diy plumbers on this forum such as myself to be able to see this drawn out so they and I could better understand S-trap vs P-trap vs arm length. Since traps are one of the more visible and accessible(such as under the sink and at first glance looks pretty mindless) to a diy homeowner, it is one of the things they will try to mess with and probably screw up. if you could make a diagram of an S trap with the trap arm 10x the diameter from the wier I'd like to see that. You would have to build your own trap right? or could you create this from a 'trap' available off the shelf? I guess we would have to define 'S-trap' to start with.
    Last edited by mrbeing123; 12-07-2012 at 09:22 AM.

  8. #8
    Forum Admin, Expert Plumber Terry's Avatar
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    Some of the old plumbing books should have been retired years ago. Time and experience has been changing the way we do things.

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