How do I rough in two toilets which will sit back to back. Can they both go to same drain?

Yes

Short answer by Joy but a correct one. If wet vents are allowed in your area you will rough in the drainage like this, (see image) and connect them to a common branch,( located in the wall and running to a vertical stack vent) either with wyes or combination wye and eight bends. Both bathroom groups will be wet vented by their lavatory roof vents. Good luck, Tom

If the toilets are back to back on a vertical stack you can use a sanitary cross with the top of the cross venting both toilets as long as they are top fixtures,any lavs, tubs, or showers must come off below the cross. In almost any situation you can use the same drain for both toilets, only the venting would change.

Hey Puff,
While I'll use a san cross on back to back lavatories I like to stagger my outlets on toilets. The reason being that one toilet will discharge directly into the other.
Staggering the outlets gets away from that. Now if we're talking double wyes or combos I could agree with that but not a cross.
Regards, Tom

Hi Tom: I see your point, but I have never had a problem with a sanitary cross on back to back toilets. The code in Ohio will not allow you to use a double wye or a doule wye with st.45's anywhere on back to back fixtures regardless of what the fixture is, because the top of the double wye, which would be the vent is lower than the inlets of the double wye of the fixture they are receiving waste from, which in Ohio is an illegal vent. I agree a double wye is a better job and also easier to snake if need be, but it is considered an illegal vent here.
Regards Puff

the top of the double wye, which would be the vent
Each half of the double wye would pick up each toilet which would be vented through the lavatory roof vents or aren't wet vents allowed in your code? And for the life of me I don't understand why discharging one toilet into another one would be better then directing the flow into the branch with an double wye or combo? And what's this business of taking the vent off a wye? Do you mean roll the fitting up on a 45 degree angle and use it for a toilet vent?
Educate me, I want to know if something new is out. Thanks Puff, Tom

A double wye may be used if the fixtures coming off the double wye are vented seperatly or run as separate branches and back vented, then the top of the double wye could be used to go out the roof or to pick up fixtures up above. Wet vents are allowed under certain circumstances when all fixtures on wet vent are on the same horizontal level. The lav vent jpg attachment you show would not be legal. The lav would have to be a 3 by 1 1/2" y off the 3" branch and vented by itself. Then you could take a 3" by 2" by 2" branch and use the shower vent as a vent for the toilet. You could not take a 2" by 1 1/2" off the shower branch and use the lav to vent the toilet. The example I gave above with a sanitary cross was for a vertical stack with back to back toilets with no fixtures above it. I am not stating that discharging toilet back to back is better than your way only that is what the code is in this area. This code has been in effect since 1998. I hope I was able to explain this clearly.
Regards Puff Thanks Puff, You explained it just fine but I'll still stagger back ton back toilet outlets. Thanks for the info. Tom

Similar Code requirements, as explained in Puffmugs' post apply in California. We are required to use Sanitary Cross fitting. Both toilets can share 1 (one) 2" vent. Milo
Would that mean that every fixture has a individual vent that's revented back tom as single roof vent? It would appear that a plumbers job is much simpler here in Florida then in either Ohio or California . I remember the fights I used to have with Growler about a counter top air gap as per against a high loop. Cheers, n Tom

Oh me , Oh my!! Is it necessary to use two separate vents? I had planned on just using one. Things are getting more confusing, guys.

Is it necessary to use two separate vents? This will depend upon what code you fall under. In my area (Standard Plumbing Code) wet vents are allowed and the image I put up is how we do it. One bath/ one vent!
Where do you liver? Regards, Tom

Thanks, Tom. I live in rural Arkansas and do not have any codes to ablige. I just wanted no residuals. I finished it yesterday and am waiting for the concrete to be poured. Thanks for your help. This is a cool site.
Bye the way, thanks everybody for helping.
When I start plumbing the walls, I'll probably be back. :)

Is it necessary to use two separate vents? All depending on what code you fall under. What's your location? Milos code vents everything but the family dog while my code allows wet vents so you would have a lavatory vent from each bathroom group connected back together to form one roof vent as shown above. So, the work's done. Did you rough with a wet vent as I pictured? And did you use a Sanitary Cross or another fitting to join the two baths to the branch? Let me know, Tom

Tom, I am new to this site and cannot find those pictures of yours. I do not see any diagrams, except the very first one. I use a sweeping V joint to catch both toilets to the drain

That first image is what I wanted you to follow. Sounds like you used a double wye to join up both bathroom groups. Give yourself a pat on the back, a stiff drink and a week 9in Vegas. Good job! Tom

All right!! Any time you are in our area, stop by for a beer. But, if I had to do this for a living, I'd be drinking the strong stuff, for sure. Thanks again, Tom and Puff, for all your help. It took me an hour to find this site, which is awesome. Concrete is coming this evening. It will take me a week to get the walls and roof up; then it will be time for the plumbing in the walls So, I might be back. LOL

You're always welcome to come back if you need help. So far you're doing just great. Any help we can give is as close as a click. Good luck, Tom