Hello all, wondering if any of you can clarify a drain run.

Installing a stand alone soaking tub in a master bath. From the tub trap I'm about 15' from the 3" stack.

Venting has me reading and re-reading codes, etc.

Was originally planning to run a 2" pvc drain to the stack with an AAV at the tub trap (I have ventilation into the space below the tub).

My second thought, since I have the room and the pipe, is to run a 3" drain line from the trap to the stack, thinking this would give plenty of room above the water in the pipe for venting.

Since this drain run passes the w/c, if the drain and the closet bend are 3" can they be tied (wc is less than 3' from the stack) Originally I had planned to run the tub drain beside the closet bend and tie it and the shower and lav drains into the stack above the wc.

I read the 3" horizontal drain can carry 20(35) DFU and the tub is 2 DFU while the wc is 3 DFU. On the table for Traps and Arms a wc length has no limit on the IRC and a 6' limit on the UPC. The tub is given at 6' (3'6") but I would assume that is due to the drain min size of 1.5".

The 3" tied layout would be a 3" pipe sloping down from the 2" tub trap entering the wc via a combo (wc using the straight through section and the tub drain entering via the sweep) Output of the combo would sweep from vertical to horizontal via 2 45's and enter the main stack within 2.5'.

This run would look like the letter "L" from above where the tub drain run is the long lenth of the "L", the WC would be at the heal of the "L" and the stack would at the end of the short bottom of the "L".

all of this is given a 1/4" per foot slope.

Thoughts?

Thanks in advance

Master