Putting a toilet downstairs?

[Qweaver]

I'm not a plumber.  I want to put a toilet downstairs.  Can I just put a clean-out type tee in the existing drain from the upstairs toilet and connect the new toilet.  Will flushing the upstairs cause the downstairs to overflow with this setup?  I guess I need to get a book on plumbing.  I've taken a lot of classes on construction but none on plumbing.

[SamB]

I'm not a plumber either, but have done some plumbing. I have toilets on different levels plumbed as you're proposing and have not had any issues. As an old plumber by trade once told me $h#* flows down hill, unless there is a backup or blockage in the main line there shouldn't be any problem. Also needs to be vented.

[pabst79]

Send me a pic or drawing and I will gladly sketch it out for you, make sure you make your tie in with long sweep fittings and make sure its vented properly and it shouldn't be an issue, unvented toilets can be a real pain, people will waste hundreds on drain cleaning bills before someone realizes it just not getting enough air.

[Kellyj]

If tying into the main 3" or 4" line, use a "Y" with a street 45.
If the toilet is within 5 feet or so, no extra vent should be needed, the main line "should" be vented.
I'll assume, if you're doing a toilet, you're also doing a hand sink, vent will be required for that, and that could also vent the toilet if need be.