Correct use of a double wye

[Mike Garrod]

does anyone use double wyes to plumb a typical bathroom group? I have seen them used 3" center ports w/ 2" side outlets, toilet obviously on the 3", and one port directly to shower and other port to lav with the lav wet venting all the toilet and shower. My question is, is it allowable to use a straight 3" double wye and bush down the center port and one of the side ports and use the other side port for the toilet? Or does the toilet HAVE to be using the center port?

 

[Terry]

The toilet can be on a side port in most codes. The bowl is designed to siphon, so treating it like it needs a santee on the vertical is not needed.
The lav and the shower do need to be installed to "prevent" siphoning.

 

[Sponsor]

 

[Mike Garrod]

So would this layout work?

 

[Mike Garrod]

2" to the lav and 2" to the shower/tub

 

[hj]

Not likely, because the shower is connected to the toilet BEFORE the vent.

 

[Mike Garrod]

Not likely, because the shower is connected to the toilet BEFORE the vent.

So what about this?

 

[Terry]

If the shower is vertical before the trap arm, you will need a vent there. Venting comes off the top of the trap arm, not below.

 

[Mike Garrod]

If the shower is vertical before the trap arm, you will need a vent there. Venting comes off the top of the trap arm, not below.

This is all in the ground. I'm not good at drawing. so this is right, isn't it?

 

[Terry]

If that is in the ground, then the lav is wet venting both the shower and the toilet with 2",

 

[Mike Garrod]

And that is good, right? Knowing that this is ground work, would that make my first example with the double wye permissible?

 

[Terry]

With the first one, I would not do a double wye, but have the wye downstream. Entering downstream is always better with toilets.
I prefer single wyes in groundworks anyway so that I can give them that slight tilt on the fitting. It's impossible IMO to not tilt the wrong way on one side of a double wye laid in the ground.