[thegk]

I'm getting ready to finish my basement the first thing I want to do is add a bathroom I didn't get any plumbing roughed in, but I do know where the main drain is in the floor, can I tap into that for the drains and also how does it need to be vented

[speedball1]

im getting ready to finish my basement the first thing i want to do is add a bathroom i didnt get any plumbing roughed in, but i do know where the main drain is in the floor, can i tap into that for the drains and also how does it need to be vented

Yes you may Wye or Combo off the main to pick up your bathroom group.
If wet vents are allowed in your area here's how it should go down, (see image) You will have to run a vent from the 2 X 1 1/2" sanitary tee on the lavatory. This vent must,
1) be run through the roof
2) revent back to a existing roof vent in the attic
3) revent back to a dry vent at least 6" over that fixtures flood rim **OR
4) if allowed or no permit will be pulled and the job not inspected you can vent with a AAV "see image" and vent the entire group at the lavatory,'
Your choice, Good luck, Tom

[massplumber2008]

Hi all..

I am very confident that Tom meant that you can WYE off the main drain or as mentioned you can install a combination wye and 1/8th bend fitting into the main drain line to pick up the bathroom group. You cannot install a TEE fitting off a horizontal drain line!

Let us know if you need more help on cutting into the drain pipe, etc...

Mark

[speedball1]

Yes, I did mean a wye or combo, Thanks for the back up Mark.