In the process of plumbing the second floor bathroom in a log home.
Question, due to the design of the first and second floor bathroom the main drain line has to be teed between the tiolet and shower about center between them.

What do you prevent the tiolet water from entering the shower?

3" drain tiolet 2" drain to shower.

Rather than a Tee you should be using a wye. Maybe Speedball1 will see this in the morning, he has pics and does better rough ins.