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Thread: Slow draining tub a vent issue?

  1. #1
    DIY Junior Member diyright's Avatar
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    Default Slow draining tub a vent issue?

    To make a long story short; I have a slow draining tub. It has been this way since I bought the house. It is a ranch built in '78. I plunged, and snaked the drain with little success. It was still slow draining but not as bad. A few weeks later it was right back to where it began. I got fed up yesterday and replaced all of the 1 1/2" pvc from the stack to the p-trap, only to find that the old was not clogged. I realize while replacing the old drain, that there are an awful lot of turns and it is a bit of a long run to the main stack. Now I'm wondering if this is a venting issue. I could use some advice. If it is a vent issue, are there any easy fixes? Or do I need to run a vent stack up to the attic and then 45 it to the main vent, or make a new one through the roof?

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    Last edited by diyright; 12-20-2012 at 12:55 PM.

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    Forum Admin, Expert Plumber Terry's Avatar
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    That tub drain is not vented.

    The vent should come off a the same level as the p-trap.
    Not that the draining would improve if you do, but you would stand less chance of siphoning the trap when the tub drained.
    Last edited by Terry; 01-02-2013 at 04:59 PM.

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    DIY Junior Member diyright's Avatar
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    Thanks for confirming Terry. A few questions; 1 1/2" or 2" on the vent? Can I use a T, or should I use a combo(Can I get an 1 1/2" x 1 1/2" x 2" combo?)? Can I angle it back to the main vent once I reach my attic, or should I just make a separate vent through the roof?

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    Forum Admin, Expert Plumber Terry's Avatar
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    For a tub,
    2" on the waste
    1.5" on the vent

    Most tubs are run with 1.5" traps and trap arms.
    It would make more sense to 45 the pipe below the waste and overflow into a p-trap, if that allows you to vent the trap arm properly.
    You are only allowed 1/4" drop per foot on the trap arm, with max distance to the vent being
    1.5" trap arm, 42"
    2.0 trap arm, 60"
    For instance, the drop on the 42" trap arm would be 7/8" at the max and 1-1/4" max on the 2.0"

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    DIY Junior Member diyright's Avatar
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    Thank you for the advice Terry! However, what do you mean "45 the pipe below the waste and overflow into a p-trap"? Are you saying to 45 past that beam from the tub, then into the p-trap?

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    DIY Junior Member biffnh's Avatar
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    I had a customer with the same problem and my first thought was improper venting, but since draining did improve somewhat after snaking (or his application of drain cleaners), I figured there had to be something in the drain mechanism itself that was causing hair to build up. Sure enough - after getting access to the brass drain I took it apart and found a small kid's toy wedged in the drain. There was no way to see or feel it without taking the mechanism apart. Now for the first time in over ten years it drains beautifully. A plumber he had look at it a few years ago told him it needed more venting and would require a large investment in re-plumbing.

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    Moderator & Master Plumber hj's Avatar
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    The lack of a vent by itself would NOT cause bad drainage, in fact it usually causes the drain to work too good, and that can cause odor problems. Your drain line IS vented through the vertical pipe it attaches to, but the line from the tub to the connection is longer than it should be, but that would not cause your problem. You also appear to have created an "S" trap with the upward "jog" but that is also not your problem. Your problem is probably at the tub itself.
    Licensed residential and commercial plumber

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    DIY Junior Member diyright's Avatar
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    Thank you HJ. So adding a vent will not help my situation? Good to know, as I was planning on adding a vent soon. Also, there is no upward section, it's just the angle of the picture. Is there anything you would recommend?

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    Moderator & Master Plumber hj's Avatar
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    quote; Also, there is no upward section, it's just the angle of the picture.

    The first picture shows the left hand pipe below the joists, but the pipe to the "P" trap appears to be "between" the joists, and if so, the only way that could happen is for that 10 or 16 inch piece to run uphill. From your picture, I cannot see any piping problem which could cause slow drainage, which is why I suspect the problem is in the tub's drain assembly itself.
    Licensed residential and commercial plumber

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