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Thread: Basement Bath

  1. #1
    DIY Junior Member Al G.'s Avatar
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    Default Basement Bath

    My basement has a typical 3-piece bathroom rough-in. The vanity and toilet are along one wall and the bathtub drain is along the opposite wall. The stub out for the vanity tees into a 2" PVC that goes into the floor and a 1 1/2" PVC extends vertically to tie in with the vent in the laundry room above (confirmed with pre-drywall photos). The bathtub drain is a 2" PVC that extends about 3" up from a plastic housing/cover embedded in the concrete. I cut open the plastic and the PVC goes into crushed stone about 8" below floor level. No trap in sight. The center of this pipe is about 63" from where the finished wall will be on the vanity/toilet side. Seems a little far but manageable.

    Would the bathtub trap typically be below the crushed stone? I'm a little hesitant to cut the cap off the pipe to check just yet since so little extends above the floor. I assume there is a trap and that the entire bath is vented by the vent extending up from the vanity drain. Is that reasonable? If I understanding venting correctly, if there is a trap then I can't run a vent upward from the PVC since it would be upstream of the trap. Thus my assumption that it's wet vented from the other vent pipe. If there's not a trap then would I put the trap in the floor cutout, tee into the 2" PVC and then extend the vent upward to tie in with the other vent pipe?

    I'm considering putting in a shower instead of a tub. Can I put in a short horizontal (with proper slope) and then turn to vertical within the floor cutout, thus putting the shower drain toward one end of the shower? Alternatives would be to run the horizontal above the floor to the center of the shower pan, requiring the shower floor to be a step up from the main floor, or to cut into the concrete to run the horizontal just below floor level.

    I appreciate your thoughts.

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    I would be inclined to think that it's a 2" stub ready for a santee with p-trap and that the vent still needs to be run.
    Only digging down more will give you more of a clue.

    Swan makes a shower pan that is 60x32 with either a left or right hand drain.

  3. #3
    DIY Junior Member Al G.'s Avatar
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    I'll dig a little this weekend and see what I find. The more I look at it and think about it the more I think you're right. It also explains why the side to side spacing between the toilet and tub is tight. The final tub/shower drain location won't be in line with the stub.

    Would I use a 2" p-trap and 1 1/2" vent?

    The vent from the vanity is vertical to the floor joist and then runs horizontal about 3 feet before going vertical again through the floor above. Can I tie into the horizontal run?

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Logically, the 2" riser at the tub is for the tub connection and the "P" trap is under the gravel, where it should be. The 1 1/2" vent at the sink is undersized for many areas, but it depends on your code's requirements. You do not have to "dig" anything. Just remove the cap or plug from the riser and pour some water down the pipe, the look down it to see if it is retaining water in a trap.
    Licensed residential and commercial plumber

  5. #5
    DIY Junior Member Al G.'s Avatar
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    I cut the cap off the 2" tub drain and poured some water in. It did retain the water. It looked like the p-trap was only a couple of inches below the gravel so I dug a little and confirmed. So I guess this is my drain and no further venting is required.

    Since we're putting in a shower instead of a tub we're moving the shower a little further from the toilet than where the drain would have forced the tub to be. It would have been right at 15" from the center of the toilet. We're also going with a little wider shower since we're just expanding into what would have been dead space beyond the end of the bathroom. This will put the shower drain toward one corner which should be fine since the shower pan will be constructed on site and tiled.

    Anything here that doesn't make sense?

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