Connecting two 3" horizontal drains to a vertical stack.

[Tony1997]

Hello_
I'm trying to find out if it's feasible to change the layout of a bathroom I'm renovating. It's a 2nd story bathroom with a shower, toilet and double sink vanity. Currently all fixture go into a 3" horizontal drains that drains into a vertical 3 or 4 inch stack. Shower and toilet each have a 2" vertical vents and lavatory has its 2" vent. All these vents join in the attic and go out of roof as one pipe.
My plan is to move the toilet next to the vanity on one side and put a tub next to shower on the other side. The easiest way to do this is to have one 3" main drain for tub & shower coming from left and another 3" for toilet and sinks coming from right both draining down the vertical main drain. I will include 2 drawings of what the lay out is and what I'm trying to change it to. Excuse my drawing skills (or lack there of). If it doesn't work I'll try to find a software to draw them better.
Questions:

1. Can two 3" drains come from opposite directions and drain into one vertical pipe of similar diameter? (Both stacks will have 1/4" per foot drop)
2. Do I need a separate vent pipe for tub or could the vented shower line vent the tub?

Note: the 2" vertical vent goes to shower drain right after its P trap which would then turn right and convert into a 3" pipe. The tub drain will join the 3" pipe then and there is no more than 16 to 18 inches from where the vent for shower connected to the shower line to where the tub line attaches to the 3" pipe.

Drawing#1 is how it is now and the #2 is what I'm trying to achieve if possible.
Thanks

&

 

[Terry]

The shower vents the tub and the lavs vent the toilet.
I would drop the toilet and lav line down with a 90 at the stack, add a 3x2 wye below that to pick up the shower and tub.

 

[Sponsor]

 

[Tony1997]

The shower vents the tub and the lavs vent the toilet.
I would drop the toilet and lav line down with a 90 at the stack, add a 3x2 wye below that to pick up the shower and tub.

Thank you Terry. That sounds great. Have a nice weekend and enjoy the sun (I'm in Bothell too)

 

[Tony1997]

Actually, one more question; after checking out the area where the 2 horizontal drains connects to the main vertical stack I'm wondering if any of these other fittings (in the attached picture) could work. Only cause adding 2 fittings on top of each other means I have to build a small box around it that lowers the ceiling a bit more in that spot. If none of these 4 could work, I'll go with your original solution. (Of course if #3 or #4 are used I'd have to cap the branch on top).
Thanks

 

[wwhitney]

Some terminology: a stack is a vertical drain at least 8' tall (or maybe it's one story). So your thread subject should be about connecting two 3" horizontal drains to a single stack.

As to your latest question, 1 is out as the side inlet has no slope. You could use a side inlet san-tee and cap the top, as long as you confirm the side inlet has the same slope as a quarter bend of that size. I hear 2 is frowned upon because when snaking it is easy to end up going straight across, when the desire is to exit going down. If you installed an accessible cleanout below, I assume that would alleviate that downside. If 3 is a double combo, that's basically the same as 4, since you are coming in horizontally on both sides, and either would be fine. If 3 is a double fixture fitting, I'm not sure if that's much improvement over 2, as far as snaking.

Cheers, Wayne

 

[Terry]

2 and 3 are out. When the toilet is flushed, the poop and water will skip across the fitting and wind up on the other side. Toilet manufacturers warn and stress to not use those fittings.

 

[Tony1997]

Some terminology: a stack is a vertical drain at least 8' tall (or maybe it's one story). So your thread subject should be about connecting two 3" horizontal drains to a single stack.

As to your latest question, 1 is out as the side inlet has no slope. You could use a side inlet san-tee and cap the top, as long as you confirm the side inlet has the same slope as a quarter bend of that size. I hear 2 is frowned upon because when snaking it is easy to end up going straight across, when the desire is to exit going down. If you installed an accessible cleanout below, I assume that would alleviate that downside. If 3 is a double combo, that's basically the same as 4, since you are coming in horizontally on both sides, and either would be fine. If 3 is a double fixture fitting, I'm not sure if that's much improvement over 2, as far as snaking.

Cheers, Wayne

Thanks for the correction, I should stop using terms I don't really know much about. I changed the stack to drain. Also thanks for the tips.

 

[Tony1997]

2 and 3 are out. When the toilet is flushed, the poop and water will skip across the fitting and wind up on the other side. Toilet manufacturers warn and stress to not use those fittings.

Thanks again Terry. That leaves me with #4 which could work just fine.

 

[Hilld]

I have a similar question as I will have 2 horizontal drains coming from different directions to the main stack. Can you use a street elbow at the top with a san T below, something like this. The top elbow would drain the shower and toilet, the San T, would take the bath lav, washer and kitchen sink (coming from a different direction).

 

[Terry]

Your top fitting is a medium sweep which works for horizontal to vertical.
The santee also works to receive from a horizontal line.

 

[Hilld]

Thank you. Very much appreciated. This site is a wealth of information. I love it.