Going to assume that C is incorrect because of no immediate vent pipe; that leaves A or B.
Which one would be the best configuration ?

Thanks,
Arky

I'm in Arkansas.

I've posted this on several other forums and so far, the B's have outnumbered the A's.

The A proponents mostly say that it's a straighter shot, thus less chance of clogs.

The B proponents say that the A allows too much rush of water, thus restricting the vent.

I'm still 'up in the air' about which one to go with, but, not being a plumber,
if left to my own impression, I would probably have chosen A.

Why would A be prohibited ?

(By the way, the main stack is also the main vent)

Thanks,
Arky

In addition, in fig A the fixture arm is attached to the main stack by means of a Wye. Code prohibits installing a Wye on a vertical stack except when attaching a vented branch.

I have attached a drawing showing the completed solution for your project. As you can see, it is much simpler than your first proposal.

Begin by attaching the watercloset on a 3" closet bend with a 2" low heel inlet and a 3" line to the main stack. Connect to the stack with a tee.

You may then run a 2" line from the closet bend up to 8' to the tub P-trap, which is under the floor. You then extend the tubs waste & overflow outlet down through the floor to the P-trap.

The kitchen drain & vent as shown. In your drawing you had concerns about 66" from the kitchen trap to the vent/stack. Under the IPC the proper size for a kitchen sink drain line is 1-1/2" which would allow you 6' (72") maximum developed length (actual length of the pipe) from the trap weir to the vent opening. Code also allows us to increase the pipe diameter by one nominal trade size, which would then be 2" and that would allow a maximum length of 8'.

Under the International code the vent may be reduced to 1/2 the diameter of the line being served but not less than 1-1/2", except vents serving a watercloset must be a minimum of 2". If the TDL (total developed length/ actual length of the vent pipe exceeds 40' from the trap weir to the vent opening on the roof, the vent line must be increased by one nominal trade size.)

The main vent MUST terminate through the roof.

Now not on the lower right hand side and you will see the Main Cleanout. Code says that you must have a main cleanout within 3' of the point where the main drain exits the structure. The main cleanout is the official point of demarcation between the house main drain and the house sewer and that is important because code allows different materials for the main drain & house sewer.

Thanks,
Arky

What makes these two arrangements not meet code, and how then would the toilet have to connect to meet code ?

Thanks,
Arky

Thanks,
Arky

Toilets cannot have vertical riser.

If there is an obstruction that prevents you from doing it in the manner I described, then kindly either explain the obstruction or post a photo and I can work out a solution.

in your last illustration you state that both the tub & lavatory have their own vents. The question then becomes, how are you venting the bath becaue you may not have a horizontal vent line until the vent reaches an elevation at least 6" above the flood level rim of the highest fixture served by that vent.

You also seem to be insistant upon running the horizontal main drain about 2ft below the floor in a crawlspace. In a crawlspace the drain should be kept as close to the floor as possible, preferably in the joist bay to prevent frost closure in winter.

It can be a PITA, but if the pipe must go there, you can get through anything.'