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Old 01-11-2017, 12:36 AM   #1
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Can a bidet share the drain of a bathtub?


We're having a bathroom addition built. There's already a drain in the concrete foundation for a bathtub. We've decided to add a bidet next to the tub. But the plumber says the bidet drain can't simply attach to the bathtub drain flow (requiring minimal concrete breaking) and instead has to go down 4 feet to the main drain (requiring major concrete breaking). Something to do with needing separate drains and a trap?

Are they right? If so why, as a bidet is essentially like a vanity sink, not a toilet.

(USA code)

Thanks!!

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Last edited by Starglider; 01-11-2017 at 12:47 AM.
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Old 01-11-2017, 08:32 AM   #2
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Re: Can a bidet share the drain of a bathtub?


I assume a bidet has a built in trap like a toilet does. I've never seen one in real life, so I don't know if the bowl stays filled or not. It will have to tie in to a drain with proper venting no matter what. I doubt you can legally tie into the tub drain past the trap, due to code assuming that all fixtures must be able to drain at the same time. Practically, it should work fine as long as you don't drain the tub and flush the bidet at the same time. If you don't want to tear up the concrete, you might want to get a bidet seat for your toilet.

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Old 01-11-2017, 03:22 PM   #3
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Re: Can a bidet share the drain of a bathtub?


Yeah, go with the bidet seat, or just run a piece of flex copper from the toilet supply up behind and under the toilet seat. Put a quarter turn valve on the PNA washer and locate it where you can reach it easily. You'll have to aim the copper tube yourself.
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Old 01-11-2017, 05:32 PM   #4
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Re: Can a bidet share the drain of a bathtub?


What state do you reside in? Currently 3 plumbing codes are used in the USA. Under IPC if the tub has a vent you can tie the bidet into the same drain line if it is 2 inch in size.
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Old 01-11-2017, 05:34 PM   #5
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Re: Can a bidet share the drain of a bathtub?


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Originally Posted by Ghostmaker View Post
What state do you reside in? Currently 3 plumbing codes are used in the USA. Under IPC if the tub has a vent you can tie the bidet into the same drain line if it is 2 inch in size.
State is California.

The tub has a vent.
I believe the tub is 2" drain.
Bidet drain is 1ĺ".

Where does that leave us?

Thanks!!
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Old 01-11-2017, 05:46 PM   #6
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Re: Can a bidet share the drain of a bathtub?


In trouble!!!! UPC is not my animal to tame. Not to worry their is a good UPC plumber that visits.
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Old 01-11-2017, 06:14 PM   #7
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Re: Can a bidet share the drain of a bathtub?


I'd be fairly surprised if the tub has a 2" drain. I'd guess it's an 1 1/2" drainpipe. You're allowed 3 fixture units on a 1 1/2 horizontal branch.

There's a distinction made between bidets with 1 1/4" drains and 1 1/2" drains.

A bidet with an 1 1/4" drain counts as 1 fixture unit which (adding the 2 for the bathtub) means that you would be able to share the 1 1/2" horizontal branch.

A bidet with a 1 1/2" drain counts as 2 fixture units and would not be legal to add onto the 1 1/2" pipe that the tub drains into.
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Old 01-11-2017, 06:19 PM   #8
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Re: Can a bidet share the drain of a bathtub?


Does that apply to California?

Here's the bathtub drain:


Space on the left is where we want bidet to go

Thanks!!
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Old 01-11-2017, 06:57 PM   #9
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Re: Can a bidet share the drain of a bathtub?


Drain pipe measurements are taken in inner diameter. So if the outside is around 2", it's an 1 1/2" pipe. If it is in fact a 2" pipe, you should be fine to use it.

The drain fixture units I mentioned are for UPC which would apply to you. The bidet you're using would have to allow a 1 1/4" minimum drain size and it would have to be piped in 1 1/4" into a 1 1/2x1 1/4 wye without exceeding the maximum trap arm length (30 inches for 1 1/4") to the VENT (not to the wye).

So you see it's possible but there's a lot of if's.

Edit:
Looking closer at your second picture. Is that horizontal pipe turning down into the ground? Is that a p trap? I'm not at all sure it would be alright to drain into the line BEFORE the tub's trap. I was imagining two separate p traps with their trap arms combining.

Last edited by BlackTiger; 01-11-2017 at 07:14 PM.
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Old 01-11-2017, 07:12 PM   #10
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Re: Can a bidet share the drain of a bathtub?


Cool.

The bidet is 1 1/4 inch drain.

So this applies:

"would have to be piped in 1 1/4" into a 1 1/2x1 1/4 wye without exceeding the maximum trap arm length (30 inches for 1 1/4") to the VENT (not to the wye)."

Looking at our photo above, and assuming the bidet on the left wall in the space, and that the vent is on the far right wall, would that be OK? I'm not clear where the 30" needs to be.
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Old 01-11-2017, 07:20 PM   #11
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Re: Can a bidet share the drain of a bathtub?


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Originally Posted by Starglider View Post
Cool.

The bidet is 1 1/4 inch drain.

So this applies:

"would have to be piped in 1 1/4" into a 1 1/2x1 1/4 wye without exceeding the maximum trap arm length (30 inches for 1 1/4") to the VENT (not to the wye)."

Looking at our photo above, and assuming the bidet on the left wall in the space, and that the vent is on the far right wall, would that be OK? I'm not clear where the 30" needs to be.

Bidet on left wall. Drain on right wall (black pipe). Tub is center.

Room is 8'8" wide.

Thanks!!
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Old 01-11-2017, 07:28 PM   #12
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Re: Can a bidet share the drain of a bathtub?


From your plans that looks like it would be way too much trap arm. The trap arm is the horizontal distance from the end of the trap "u" to the vent.

There's not really anything you could put that far away from its vent.

To explain the reason why is that the vacuum isn't broken until it reaches that vent on the right wall. So you've got here, let's estimate 7 feet of pipe until the vent. If that pipe fills with water while draining, all that water weight will suck the water out of the p trap and draw air through the (now open) bidet in order to relieve the vacuum. I don't really know what a bidet is but even if it is like a toilet and has a bowl of standing water, that water will get sucked down the drain and you'll hear gurgling and sucking noises. And once the trap is dry, sewer gas will come up your drain pipe and into the room which is both gross and eventually a hazard to your health.

In order to have a drain on that wall, you will need additional venting.
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Old 01-11-2017, 07:46 PM   #13
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Re: Can a bidet share the drain of a bathtub?


Quote:
Originally Posted by Starglider View Post
We're having a bathroom addition built. There's already a drain in the concrete foundation for a bathtub. We've decided to add a bidet next to the tub. But the plumber says the bidet drain can't simply attach to the bathtub drain flow (requiring minimal concrete breaking) and instead has to go down 4 feet to the main drain (requiring major concrete breaking). Something to do with needing separate drains and a trap?

Are they right? If so why, as a bidet is essentially like a vanity sink, not a toilet.

(USA code)

Thanks!!
Your plumber is correct.
Maximum 1-1/2" trap arm length is 3'-6". Plus, you can't have 2 traps on one trap arm, not to mention that 3 DFU is too much for 1-1/2" pipe- unless the code has recently changed.
Best to listen to your plumber...
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Old 01-11-2017, 08:33 PM   #14
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Re: Can a bidet share the drain of a bathtub?


Thank you all!

A bidet is basically a low down sink for washing one's private parts. It doesn't have standing water. Popular in France. No wonder they have a lot of sex.

Thanks!!

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