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Thread: Question about p-trap

  1. #1
    DIY Junior Member Shelly296's Avatar
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    Default Question about p-trap

    I am running a new washer box. The original one had the water and drain on the wall. Since I have gutted the bathroom, I could install a new box, larger supply pipes, and proper 2 inch drain because that is the backside to the laundry area. When I drilled the hole for the drain line that goes into the crawl, the block wall is preventing me from having the p-trap directly below the drain. I am needing to run an elbow to get the drain out past the block wall and then run the p-trap. So, i will run the 2 inch PVC drain down about 3 feet and then put in an elbow, run about a 10 inch section of pipe and then the p-trap. So, can I run a 90 before the p-trap?

    Shelly

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    Forum Admin, Expert Plumber Terry's Avatar
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    The p-trap should be above the floor, located about 9" above.
    If you need to offset above the p-trap to the box, that is fine. I normally do that with two 45's

    If the standpipe is too tall, it can siphon the trap. That's why you don't put the trap in the crawl.

  3. #3
    Test, Don't Guess! cacher_chick's Avatar
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    If the trap was below the floor, I can't help but to wonder where the vent is, and how/if the situation will be corrected.

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    DIY Junior Member Shelly296's Avatar
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    The original trap was in the crawl space with the vent for the whole house being tee'd off of the main waste drain horizontally through the crawl and then the vent going outside the house where it ran vertically up about 7 feet. We see this a lot here around the old lake cottages; vents running on the outside wall.

    Anyway, I thought that the p-trap needed to be closer and I should have enough room in the wall. I guess I will find out tomorrow. I was thinking that I would not need to vent this drain, but if I needed to, couldn't I just tie into the drain and run it up through the wall and out the roof? I could "y" off the drain before the p-trap. Will that break the vent? Is that wrong?

    Shelly

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    Moderator & Master Plumber hj's Avatar
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    Your DESCRIPTION seems to be correct, but HOW you actually install the pipe determines whether the vent is proper or not, or even effective. But without some knowledge of venting, which you do not have, it is easy to think that all you need is a pipe through the roof without considering HOW it is connected.
    Licensed residential and commercial plumber

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    Retired Defense Industry Engineer jadnashua's Avatar
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    To be a vent, it must come off of the trap arm before the waste turns downwards after the trap.
    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 Shelly296's Avatar
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    Here is what i came up with today. And yes, the previous poster was correct, i do not know much about venting. I came out of the washer box with piece of 2 inch PVC. Then i put in a wye that is 2x2x1 1/2 inch to run the inch and a half vent to the attic and i need to check with the inspector as to what size needs to go through the roof. Then i had to use two 45's to get the drain over, put in the p-trap and then a 90 with more two inch to get through the floor and sill. Another 90 to get out over the block in the crawl.

    Shelly

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    You have not created a vent. The vent must go AFTER the p-trap, before the drain line turns down. If I understand you, you have a line branching off BEFORE the trap, which does nothing.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #9
    DIY Junior Member Shelly296's Avatar
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    Quote Originally Posted by jadnashua View Post
    You have not created a vent. The vent must go AFTER the p-trap, before the drain line turns down. If I understand you, you have a line branching off BEFORE the trap, which does nothing.
    Thank you for hanging on through my many questions. Your reply before this one was so helpful and saved me from making the mistake that you cited above. So, my new set-up is a combination of help from you and terry. Since my washer box has the drain in the middle, I took Terry's suggestion about using 2 45's to offset because the only room I have for the trap and vent is in between the two studs. So I ran out of the box with the 45's, so now I am against one stud, ran the 2 inch pipe down to the trap, where trap arm starts to bend down, I installed the 2x1 1/2 x2 san tee. The vent goes up and the drain goes down to a long 45 to the main waste pipe.

    Thanks again Jim!

    Shelly

  10. #10
    Forum Admin, Expert Plumber Terry's Avatar
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    Sounds good to me!

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