I have a 4" Iron drain / vent line that runs from a toilet upstairs down to the basement and then in the basement concrete slab out. There already is a tap about 24" above the slab for a kitchen sink. I'd like to add a bath in the basement and tie into the iron pipe. I can chip out the concrete if needed. I'm thinking I would tie into the drain line for the tolit and bath with a new tap od some sort and tie into the kitchen drain for the sink. I most likely will use a plumber to do the rough in of piping but want to get informed before I start talking to them. What would you sugest to do this the easiest way but have a good installation.

That 4"line from toilet upstairs is not a vent its drainage You can tie into the slab drainage for bath and toilet sink If you proper fall The new toilet should be vented 2" pipe within 3' of closet flange Sink should be 1 1/2 "T" down for drainage Up for vent Tub also vented tie vents together and up through floor and out roof. This Vent is a must and do not use your 4"cast as a wet vent. Improper vent slow flusf and drains (CLOGS)
Good Idea getting a plummer
Hope this helped Signed 21Boat

That 4"line from toilet upstairs is not a vent its drainage You can tie into the slab drainage for bath and toilet sink If you proper fall The new toilet should be vented 2" pipe within 3' of closet flange Sink should be 1 1/2 "T" down for drainage Up for vent Tub also vented tie vents together and up through floor and out roof. This Vent is a must and do not use your 4"cast as a wet vent. improper vent slow flusf and drains (CLOGS)
Good Idea getting a plummer
Hope this helped Signed 21Boat

Thanks for your reply. The 4" pipe goes up from basement, has a tee to toilet upstairs, and then goes up all to the roof where there is a vent. The other end of the pipe is a drain that goes under the slab. So the iron pipe is a staright run from the roof to the slab that has a tee for the toilet & sink upstairs and another 2" copper pipe from the kitchen sink downstairs. Hopefully this is clear now.

My thought was to tie into the 4" pipe by either building a false floor and running under it or by chipping up concrete if I have to. Is there a way to tee into the pipe without cutting it to install a fitting above the slab. The pipe is inside a closet so it is well exposed. I may demo the closet wall since I am putting in new walls for the bath.

Yes you have to cut the pipe to tie into it. If that "straight run" has anything hooked into above your new bathroom that's a wet vent no no. The vent for this new bathroom has to have a dedicated vent and be above and free of any drainage from above. Keep in mind A vent has to be off that 4" sewer line from the new toilet that vent will be right after where you set the toilet not a before thing which is in the wet vent zone any drainage that is used to also vent a pipe is bad flow for water (CLOGS) later