When the kitchen or bathroom sink drains it goes into my bathtub. I'm not sure why.

Hi Halo...

The sinks and the tub drain connect together and then go into the larger toilet drain pipe. The drain line is clogged between the toilet drain and the tub drain.

Rent a small electric hand-held snake and purchase some leather gloves and safety goggles and snake the drain from the kitchen sink or from the tub drain overflow hole. You shouldn't have to snake too far...

If you snake down the tub overflow plate you'll run into the PTRAP about 18" down... you'll need to run the snake while pushing on the snake to persuade the snake through the ptrap. After that it should go pretty easy. Check out the video below.

If you snake through the sink drain hopefully you will find a cleanout under the sink. This will be easiest if you don't have to go through a ptrap.

Keep water in the tub so you'll know when you hit the clog... when it starts to drain you'll want to really work that snake forward and backward multiple times at that spot when the tub started to drain.

Any questions... let us know, OK?

Mark