I have a 110 year old house that in the 3rd floor attic has a small apt. The drain from the Kitchen sink connect wtih the bath tub drain–when the Kitchen sink drains it come sup into the bath tub. The toilet and bathroom sink drain quickly. I believe ther is a blockage in the joint pipe before it connects to the vertical stack. I put a couple of very stang drain cleaners down ther and it helped a bit. I tried to put a snake in but couldnt get it around the bathtub trap. Cant access from below without pulling down the plaster ceiling.Any suggestions–I cant take the trap off from the top either. I put the snake down the bothtub overflow.Appreciate any help or suggetions yu can give