Water softener drain did not work

[Smac]

I am installing a water softener, the floor drain is too far so I decided to tap into an existing drain from an upstairs bathtub drain. I put in a T with a p trap and a vertical pipe. All of this is 1 1/2 black pipe. The problem is when I turn on the bathtub water comes out through the new P trap and drain for the water softener. See picture.View attachment 1642457155425.jpeg

 

[RS]

Both of my water softener drains are piped directly into a drain pipe with a saddle fitting, has been working fine like that for many years. One of them drains into the kitchen sink drain below the trap.

 

[Twowaxhack]

You have a pipe obstruction farther down the pipe. You’ll need to have that drain cleaned out.