Submitted by Fantastic_Seaweed978 t3_11z6614 in DIY

I know very little about plumbing, but my p-trap started leaking so I bought a replacement. After installing, I realized it looks like the physics of this won't work:

Doesn't the drain pipe need to be below the entrance of the p-trap? Will I have standing water all the way up that column of pipe? Just want to confirm my understanding of how this is supposed to work is correct.



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NotWorthTheTimeX t1_jdb336w wrote

You are correct. With this setup, some water will always sit in your garbage disposal and it will drain slow.

The ideal is to lower the height of the pipe the drain connects to. It looks like you have a vertical drain that goes down through the floor. Super easy to cut a section out and lower it down.


Fantastic_Seaweed978 OP t1_jdb3tpj wrote

Thanks! Thought so. Yep you're right about the vertical drain pipe through the floor, I'll look into doing that


diablodeldragoon t1_jdb3660 wrote

Yes, the water will level out. As long as it's not backing up or draining into the disposal, it should be ok ish.


OldFashnd t1_jdb3qyn wrote

it isn’t technically useless. The point of the p trap is just to keep the bad smells of your plumbing from coming back up through your drain pipe. This will still accomplish that. Your water level will raise up to the point of the drain pipe though, meaning that your garbage disposal will have some standing water in it, which may create it’s own smells, and will probably cause corrosion/mold/whatever else in your garbage disposal.

You didn’t mention changing the garbage disposal out though, so if that and the drain pipe have always been this way and you haven’t had any smells or otherwise negative consequences then it probably isn’t a big deal. It’s definitely functional as a p trap, it will prevent the smell/gas from coming up through your sink like it should


Fantastic_Seaweed978 OP t1_jdb4jbt wrote

Gotcha, yeah I guess it technically does function as a p-trap. My understanding is that ideally, only the bendy pipe should hold water instead of the vertical pipes.

I was also thinking about what caused the old one to fail in the first place, since the washer on the lower part had completely detached from the pipe. My thought was maybe it's holding more water weight than it was designed for? Could the friction fit be failing because the column of water is too high?


OldFashnd t1_jdb83dx wrote

Agreed, this setup is definitely not ideal. If it was me, it would get put on my to-do list of things that need done, and then it would sit at the bottom of that last and never get done because other stuff takes priority lol

In other words if you’ve got the time and the desire to fix it, it is probably worth it. Doesn’t look like it’d be too difficult to cut the main drain pipe and plumb in a new one that is the correct height.. It will probably be fine though

Disclaimer: i am not a plumber, just a dude who has done just enough home plumbing to be dangerous


filthyziff t1_jdb42ba wrote

Interesting, I haven't seen a p trap directly after a disposal. Usually it Ts to the other side of the sink and the p trap is below the T. That way you only need one.

Do you only have that one sink basin with the disposal attached?


Fantastic_Seaweed978 OP t1_jdb4xla wrote

>Do you only have that one sink basin with the disposal attached?

No, there are 2 sink basins, each with its own p-trap: Looks like the second one is correctly installed

FWIW I've seen signs that the previous owner of this house did a lot of DIY. I'm thinking he may have installed the disposal himself without fully knowing what he was doing