Island Bathtub

Hi All
A family member presented me with an interesting problem he is working on in his house. I was not sure what I was about to tell him was correct, so i thought I'd pass by all of you experts for the real answer. (if you don't mind):

He has, in his old, old home, two island bathtubs. The walls for the tubs with the faucet & drain are only about 2" taller than the tub rims. (They are not free standing tubs. they have aprons) the faucets are deck mounted with flex hose showers. the tubs are in the "middle" of the room.

His drum traps froze and broke before he bought the house. he installed 2" P Traps on the tubs. Now, when a toilet flushes or a full tub is emptied, of course the traps gurgle and try to suck dry. I told him I thought they needed to be vented. But, in the middle of the room- how?

The best guess I came up with was to run a vent from just after the trap to the wet wall (about 4 feet away) and up, above the third floor bathroom fixtures and tie into the vent. But, the problems I see are that
A) The vent will run horizontally in the floor under the bathroom to the stack. An accessible clean out can be placed behind the access panel in the short wall. Somehow, I don't imagine that is to code, but I think it may be better than no vent. An AAV would be below the flood rim, as the wall is about tub rim height.
B) The vent would "tee" in to the tub drain almost at the point the drain meets the stack. (The stack fitting is a 3x3x3x2 Toilet, & Both Tubs) The lav sink and toilet are not vented either. but those are easy.)

I attached a drawing to help clarify. Black is existing and red is planned.

What do you all think? Adding height to the tub walls is not an option, as this tub arrangement makes the room "spiffy".

Thanks for all of your help,
Paul

You need to state where you live and what plumbing code your local jurisdiction uses. However:

You need to cut in separate vents for each tub trap then run it to a full height wall, tie them together then either tie them into an existing vent or vent through roof. You cannot tie the vents together below the flood rim nor can you use 1 vent.

Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County

Winslow said:

You need to state where you live and what plumbing code your local jusidiction uses. However:

You need to cut in seperate vents for each tub trap then

Click to expand...

If they are in an area which allows wet venting, a single vent will do.

Thanks for the suggestions!

I will check what code Detroit uses & the Wet Venting situation. But, in all honesty, he will not be permitting the job.
Why? A Couple of Examples of Our Fair City In Action- He was mortaring a hair line crack in his front porch slab and got hit for a permit. It was 350.00. Honest! He put in new grass-from-seed. Permit Required. I could give you examples from my trade, but you would not believe what I write.
The city gets enough money from the honest folks. His house purchase price = 40,000 Prop Tax 12,500 Income Tax 3%
He's just doing this job to make his house plumbing safe and functional.

Oops! Sorry, enough crabbing & back to business:
A question I'm still not clear about is since the walls are basically tub rim height, can he tee off after the trap in the floor joist space and run horizontally (following & above the tub drain) to the stack chase & up above the highest fixture upstairs for the vent connection to the stack? He will put a clean out at the tub end of the vent run should the vent clog.

It is the running horizontally while below the floor rim of the fixture that concerns me.