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Thread: Tub drain Venting

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  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.

  6. #6
    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

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