A trap arm for a toilet can't exceed six feet.
That's from the flange to the vent.
"I'm not a pro plumber, but as long as the maximum distance between the toilet (built-in trap) and the stack/vent is not exceeded for 3", it should work fine, assuming that all is sloped 1/4" per linear foot.
Call your Building Inspection Department for local code on the max distance between a toilet and the stack/vent for 3".
I read this in an earlier post and I have some questions along these lines. Does the above mean that the max distance you can run from flange to stack/vent line is 3"? What I have is I am plumibng a home and have to toilets that will be connected to 3" outlet flanges that will drop down through the subfloor about 6" and then will 90 off and run about 2-3' before dumping into the main drain line. Both fixtures are vented as such: the 2" vent line will come in at the 90 after it drops down the six inches below the subfloor. Will this setup work? Also, is one 2" vent big enough to vent both toilets and am I correct in assuming that a trap is not needed when plumbing a toilet since the toilet has a built in trap? I read in another post somewhere that Terry stated that a 3-4" pipe can run 6' (72") before the vent/drain line. If this is true, the above quoted statement really threw me for a loop and had me worried about my plans. I would really appreciate it if someone would take the time to help me out. Thanks.