There is sometimes a disinction between what is legal and what works. You have a system that is not installed to code, but it works. It was done that way to save space, and it would require major redesign to do it correctly. Redoing it the same way may even be difficult using ABS or PVC, since the fittings are larger.
: I am remodeling the master bath in my house. The two bathrooms are back-to-back.
: The toilets are back-to-back with the vent stack in the wall between them.
: They are currently plumbed with 3" copper which is 25 years old. In three places
: the copper has oxidized completely through. The neighbor who built his house
: along with mine has had the same problem with his copper DWV pipes. It appears
: to have happened in the three places where there is a horizontal run between the
: connection to the septic systems and a vent. There is nothing electrical grounded
: or connected to these pipes.
: Luckily the baths are right near where the connection to the septic system is.
: My plan is to remove all the copper and replace it with PVC. As a temporary
: solution I have cleaned off the green copper sulfate where the pipes oxidized
: through, covered the holes with heavy polyethylene, and taped it with duct tape
: clear back to sound pipe.
: My dilema right now is whether or not the back-to-back toilets are plumbed with
: the correct fittings or if there is a better way to do it. If I'm going through the
: trouble to replace it all, I want to do it the best way possible.
: Right now, the connection goes like this: closet flange to sweep 90. The 90 turns
: the run horizontal and then to a waste tee. The tee is on its 'back' where it goes
: up and vents through the roof. The other side of the tee goes to another waste
: tee which is on its back. The tee has a 45 on it which takes it to vertical and
: connects to the other closet flange. The other side of the tee goes on and leads
: to the connection to the septic system.
: I have read that you are not supposed to use waste tees on their 'back'. In my
: current set up there are two of them. The one for the vent I see no problem with.
: My question is whether or not the one that goes to the second toilet is a problem.
: I have also read that the toilet is supposed to be connected before the vent and
: not after. Another way to view it is that I have a 3" horizontal run. At the end
: is a toilet, next 3" vent, next another toilet.
: So, what is the proper/better way to plumb back-to-back toilets?
: Any help will be appreciated.