DWV dilemma

I am remodeling an existing 2nd story bathroom and plan on adding a new tub. The plan is to tie into the existing waste line (3" cast iron - horizontal run) with a neoprene sanitary tee. This tie-in is about 2 feet (down) from the existing toilet tie in. The toilet is connected to the waste line with what looks like a "y" fitting and is vented with the same 3" cast iron pipe about 5 feet on the other side.

Question: If I tie into this waste line in this manner do I need to add a separate vent line and if so where?

[I]"Fearless DIYer".......will try any project ...once!

(see attached "crude" diagram)........sorry guys but I'm no architect. Thanks for the help.

master plumber mark

you would want to install a vent or an auto air vent somewhere in the new line near the tub
before the trap to prevent the trap from siphoning..

vent

You especially need a vent there because the toilet will be draining past the tub/shower opening. And what is a "neoprene tee"? If it is a rubber one you cannot use it at all.

2 follow-up questions on venting

Thanks alot for the input guys........2 other questions:

In lieu of a neoprene (rubber) tee, I will use an ABS sanitary tee and clamp couplings to connect to the cast iron pipe......I am working between a 16" floor joist and have limited space.....so is it OK to use a sanitary tee as the tie in or must I try to fit a wye tee?

Must the vent for the tub drain be located in line between the tub p-trap and tee tie-in (highlighted in blue on diagram) to the waste line or can I locate the it between the toilet tie-in and tub tee (highlighted in yellow on diagram) - the reason I would want to put it there is because I can run the vent pipe up inside of a wall.

Thanks Again

It looks like your drains run horizonatally correct?

You can not use a sanitary tee as a drain fitting in a horizonatal run of pipe. You must use a Wye instead. Setting a tee on its back is not permissable for drains.

If you used an auto vent (Air admittance valve) [if code approved] it must be accessible and at least 4 inches above the top of the trap set back into a vent tee. Or you need to place a traditional vent no further than 3 feet from the trap.

vent

IT has to go in the blue. In the yellow it would be ineffective as a vent for the shower.