Adding a tub drain to a toilet branch

Starting a new thread - was told that I shouldn't add this to a thread that had already been started. I am remodeling an old 2nd floor bathroom and want to put the tub on the same branch as the toilet. See the picture below.



I want to put the toilet between the tub and the tub drain. I was thinking of using a long sweep with a low heel inlet to connect the tub to the toilet and then the toilet to the stack. There is a separate vent line by the tub already, so that won’t be an issue. It is OK code in Kansas City. My question is whether this works well or not – I have read that if the toilet is not always at the end of a branch, low volume toilets tend not to get sufficient suction to pull waste all the way through the toilet’s trap. There really isn’t enough clearance to put a wye fitting between the closet bend itself and the stack Tee to connect the tub on the “dirty†side. Any thoughts?
Thanks

The tub's vent must be downstream of it's trap. The sink would need it's own vent to prevent it's trap from siphoning. The low heel inlet mounted horizontally is strictly prohibited in most places.

A proper connection on the same level would require a wye downstream of the water closet (if there was room), or a side inlet tee installed in the vertical stack.

Knowing where you are or what plumbing code you fall under can be a determining factor as to what is allowed or not allowed.

It is not correct to use the low heel inlet like that, the toilet needs to be vented before anything ties in. You would need to tie into the vertical stack above or below the toilet (or use a san tee with side inlet could be used). Also, the tub is not vented right. The vent needs to be downstream from the trap and properly configured. The lavatory also needs a vent.

Sorry - I'm a terrible artist. First, let me clarify because my drawing was bad: both the tub and the shower have their own vents to the roof - I will be tied into both of them. And I know the bath vent has to be after the trap. Bad artist in a hurry. My question is really around the waste water: Maybe the picture below will be more clear:



Option A (on the left) is what I proposed. It is the easiest due to the spacing in the floor joists. The 2" soil pipe would enter the heel in the back, water would "pass" through the bend and continue to the sewer. I had read that this was acceptable and can't find in the KCMO code that it isn't legal. The only research I've found mentioned that the siphon in the toilet with a low-flow toilet tends to break earlier, resulting in multiple flushes when there's "big business".

Option B (on the right) is an alternative; I would try to fit a branch between the closet bend and the cast iron hub. The inserted wye would receive the water from both the tub and the sink. The two issues are (1) the limited space for the why between the cast and the closet bend and (2) the limited space between the joists due to the location of the stack spacing - it would probably require a lot of sawzall and bracing activity...

Option C (not shown) is obviously the worst: somehow cutting into the stack below the toilet. Problems with this are: (1) this is a second floor bathroom, so I can't really go below the level of the joists and (2) trying to cut a piece out of a vertical stack would be near impossible for me and a fortune for someone else.

Out of curiosity, this is an old bathroom, built 90 years ago. When the floor was removed, it was one of those old concrete floors with the mosaic tile on top and the lead pipes embedded in the concrete. The tub line fed directly into the closet bend very similar to option "A". The only difference was that it was a complete lead pipe and it did enter on the side (rather than directly in line) using a lead wye. Never had a problem with that - no leaks and would flush a small child if they happened to fall in! What's wrong with repeating that setup with the only change that the tub feeds from the rear rather than from the side? (Besides being PVC instead of lead?)

I should have taken a better picture, but the picture below shows the old lead toilet pipes if you look carefully. On the lower right corner of the picture, you can see the closet bend (with the beverage cup stuck in it). It's right in front of the stack. Note that the drain from the tub is entering the bend near the top). You can also see where the old tub was on the left side of the picture, with it's own vent.


Thanks

Kansas City appears to be covered by the Uniform Plumbing Code.

UPC 706.3 Horizontal drainage lines connecting with other horizontal drainage lines shall enter
through forty-five (45) degree wye branches, combination wye and one-eight (1/8) bend branches, or
other approved fittings of equivalent sweep.

Thanks, Cacher - looks like Option B and the sawzall...

Plan "B" isn't any more legal than plan "A" and there probably isn't enough room to put in a fitting anyway. Alas, "C" is the legal option.