Help with sewage backup at home. how do I find the most downline drainage point?
Any time ANYTHING runs (including flushing) it backs up into my two bathtubs. I have removed both toilets and ran a short snake (15fy) down the drain and I didn’t come in contact with a blockage. Because it backs up in the bath tubs even when something across the house is being used I think the bathrooms are at the end of the line.
I would like to get this resolved tonight and am willing to do the work, I just don’t know where to go next. Obviously I will be calling the plumber tomorrow, I would just like to be able to shower soon if I can.

if u live in the city its inbetween your house and the street im sorry i dont no wr u liv
It backs up in your tubs because they’re on the floor which is the lowest point not because they’re at the end of the line. Go outside and look for a cleanout close to an outside wall. It will be a plug with a square tang on top that can be unscrewed with a pipe wrench. Try running your snake in there first one direction and if nothing then the other direction.