Top of the day to you Tom! I am just about to finish up with my drain lines. My tub drain will need to make a horizontal run of about 11 feet before I can pick up a vent in a interior wall. Is this distance OK? Should I go to a 2 in. drain leaving the trap? Should I try to install a auto vent just after the trap? If I install a auto vent It will be very difficult for me to get it above the flood line or tub over flow if that is correct term. Thanks Tom. Have a good day. Dave.

Hi Dave, I wasn't talking about a auto vent when I said to revent above the flood rim. Install the auto vent just behind the trap on the stubout line. It can not back up even being below the flood rim. I would increase the lavatory line to 2". Better drainage that way. If your tub drain ties into the lavatory drain line you will be vented through the autovent. Keep me informed. Tom