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Thread: Very noisy bathtub drain

  1. #1
    DIY Junior Member rick112's Avatar
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    Default Very noisy bathtub drain

    Hello, my name is Rick and this is my first major DIY project and my first post to this forum.

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    I just installed a new bathtub as part of a full bathroom renovation. While draining the tub after a leak test I was surprised by the amount of noise coming out of the overflow opening. I did some research on this and other plumbing sites, and it seems the most likely cause is improper venting. The thing is, I installed a dedicated vent for this bathtub following all the guidelines specified in my DIY pluming books and the 2009 International Plumbing Code, which my state and county uses for it's local plumbing codes. All waste and vent tubing is 1 1/2" PVC and the distance from the trap to the vent is about about 14". While the tub was draining I put a piece of plastic over the overflow opening to see if it was perhaps sucking air and found no air was being pulled into the overflow. I would think that if the drain were starved for air it would try and suck it down the overflow. So I'm really confused about why it's making all that racket when it drains. Any thoughts?

    -rick

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    Retired Defense Industry Engineer jadnashua's Avatar
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    What sort of noise is it making? The fall to the trap is fairly long and that might have been shorter. A well draining tub can gurgle some as it sucks the water down. If it is the falling of the water, cast iron is quieter. PVC doesn't block much noise.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member rick112's Avatar
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    It's a popping-gurgling sound. It seems to get louder as the water level gets lower. I made an MP3 recording of it but i can't upload it as an attachment. Also, the drop from the drain T to the bottom of the trap is 14". It doesn't sound like falling water to me though. It's not a spattering or splashing sound.


    -rick

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    Forum Admin, Expert Plumber Terry's Avatar
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    They do make noise while draining.
    The piping looks fine.

    I would have run 2" to the vent, and then 1.5" to the p-trap, but that would have made noise too.
    It will work.

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    DIY Junior Member rick112's Avatar
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    Yeah, I wanted to do 2", but the original 1 1/2" iron pipe was T'd into the closet bend which I didn't want to mess around with. I ended up cutting the old drain off 6" from the closet bend and using a banded coupling to attach the new PVC.

    I guess it could be a normal draining sound if you say so. I wish I could upload the MP3 I made. It really is a loud and nasty sound.

    -rick

  6. #6
    DIY Junior Member rick112's Avatar
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    I was wrong about the overflow not sucking air. I didn't cover the two holes that are tapped through it for the screws that hold the overflow cover plate. I tried again with the plastic film over the front and my thumbs over the 2 holes in back. With the overflow completely blocked, the gurgling sound goes away and all I hear that familiar sound of water rushing through a pipe. When I uncover the screw holes I can hear air being sucked into them and the quiet rushing sound is replaced by that noisy gurgling again. The tub definitely drains slower but it's about what I would expect. It's able to make a small tornado at about 2". With the overflow sucking air and making noise, the tornado started at about 4" then turned into a hurricane.

    I thought the vent was suppose to supply the air to the drain. Is it normal for the overflow to suck air?

    -rick

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    Forum Admin, Expert Plumber Terry's Avatar
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    Either the lav overflow or the tub overflow will speed draining.

    Just for fun, do a search on vessel sinks.
    A big complaint with them is the slow draining.
    Vessels don't normally come with an overflow, so the water sticks together around the grid covering the drain.
    Add the overflow, and the water now pulls itself through the grid quickly.

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    Moderator & Master Plumber hj's Avatar
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    The "gurgling" noise you hear is how I tell if a tub drain is working at its optimum best. When it does, it aspirates air into the water flow through the overflow. The faster the water is draining the more air it draws and the greater the noise level is. A drain that makes NO noise is almost plugged up.

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    DIY Junior Member rick112's Avatar
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    For what it's worth, here's a zip file of the MP3 made.
    Drain sound..zip

    Yeah, I see a lot of complaints about slow draining vessel sinks. What about utility sinks and single basin kitchen sinks which don't have overflows, in your experience, do you find they tend to have problems with slow draining?

    I guess if there is anything in your house you want draining as fast a possible, it's you bathtub/shower. With all the dirt, soap, and oils going down there, you want to keep that gunk moving a fast as possible inside the pipe.

    -rick

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