From the information in your post it is obvious that you are under the Uniform Plumbing Code.

The UPC minimum trap size for a floor drain it 2".

If you were to install a 2" floor drain the code will allow you to increase the size of the trap or drain line by one nominal trade size, which would then be 3".

You could run the waste arm from the trap to either the stack or the WC waste line, however no matter which you choose the maximum allowable developed length of pipe measured from the trap weir to the vent opening may not exceed 6'.

Hmm.. sorry for the confusion, I should have mentioned which code I was under in my first post. I am under the 2003 IPC.

Here is a link that might be useful: Fairfax County building codes

In your original post you stated that you were allowed a 6' run on a 3" line, which would be correct under the UPC however

Under the IPC the bottom of the pipe at the trap weir may not be higher than the top of the pipe at the vent opening. From this we can then formulate a mathematic formula which is the diameter of the pipe divided by the pitch.

The code further states that all lines of 3" or less are required to have a minimum pitch of 1/4" per foot therefore the maximum length of a 3" line would be 3" / 0.25" = 12' BUT. be very careful here.

The table in the code allows a 3" line to be 12' but that is based upon the code minimum of 1/4" per foot. On the other hand, if you should run the line with a 1/2" per foot pitch the maximum allowable length would then be reduced to 6'.

Thanks! In any case I'll be having a plumber install this - I'm comfortable with the pressure side but not with cutting into a self-supporting cast iron stack. 6' is plenty to get the drain near the middle of the kitchen, so I'll let them decide what the best way to run it from there is.

Update - The plumber pointed out a couple other things. He'd prefer to go into the WC waste, but needs to wait for a callback from the local inspector. Apparently they need an exception for allowing a connection that close to the vertical stack. He also said that the drain will need to be vented regardless of length in order to be certain that the toilet flush won't siphon the trap. There's another 1.5" vent (for the kitchen sink - which isn't drained to the same stack it's vented to) that can easily be tied into and it won't add much to the cost of the job. Plus it means the drain can go anywhere on the floor, no length restriction.

Thanks again, it was very helpful to already have an idea what I was talking about when I went over this with him.

" prevent a dangerous level of bacteria building up because food and liquids were allowed to pool up and remain stagnant within your kitchen."

And I thought we had a messy kitchen! :) Haven't seen any stagnant water pooling in our kitchen for quite some time :)

Anyway.. our kitchen would be on a slab so sealing it would not really be an issue. I though we may have a very small sloped area around the drain (maybe 1'x1' or so).

Maybe it is not worth it.