Basement Question

Great forum. My basement was roughed in (unfortunately) only with drains for a sink and water closet, with a vent stubbed down from the first floor. I need to add a drain for a tub. Is it OK to set a side-inlet sanitary tee on the 3" riser for the water closet (just below where the closet flange will be), and run 2" to the P trap for the tub? I would plan to re-vent the 2" between the WC and tub drains, and also connect the vent to the sink. Or must I uncover the horizontal drain which runs to the water closet and tie into that? Thanks for any help.

Sounds like you have a good understanding of wastes & vents. If you can,it would be better to cut the 3" 90 off at the downstream side, Put in a 3" "side inlet" 90 (has a 2" cup in the side) Also called a side inlet closet bend.Bring your riser back up for the WC , pipe your lavy and shower off the 2" making sure to wet vent the group off the lavy. More work but worth the trouble in the long run. Good Luck !

Thanks for the reply Cal. I'll go ahead with the side inlet closet bend. FYI, the lav was previously run with 2" separately... I'm not sure where it ties in to the main. So I'm planning to use the side inlet from the closet bend for the tub only. I will tie the lav to the vent and plan to re-vent between the tub and WC just to be sure it's all vented adequately. Woody