I have an old house and one of the previous owners built the bathroom. There is a toilet and a shower. When I snake the shower, the snake comes out the toilet hole( I have the toilet off) There is a t down there and I checked the clean out outside and it is OK. It is plugged and I need to make the snake go around the corner of the T. It must run straight from the toilet to the shower with a t off going to the septic tank. The floor is a slab so I can't change it. Any Ideas?

What happens when you try to snake down the toilet? Most slab with septic have a clean out in the basement floor right next to a wall.

There really should not be a "T" installed in sewer pipe. Drain cleaning machine cable just won't make the turn. As said above, see if you can snake it through the toilet inlet or clean-out outside. You could also try to snake it through a vent, if it extents above the roof

Milo