I goat a call from a tenant of one of my duplex's he said that one of his toilets was cloged he plunged it out and it flush's fine now, but there is sewer backup coming up in both sides in the tub.. The rest of the house is functioning fine on plumbing any thoughts?

Need to know what fixtures are running that cause the backup in the tub. Most likely you will have to have the main drain augered.

Need to know what fixtures are running that cause the backup in the tub. Most likely you will have to have the main drain augered.

It happens when they flush the toilet..

What your tenant did when he plunged the toilet is move the clog out of the toilet and on further down the line where it's now backing up out of your tub. You have several options here.
You can snake the drain from the lavatory roof drain. Put out enough cable to reach the base and 16 feet more. **or**
You could remove the tub waste and snake from there. (see image) Unscrew and remove the overflow plate,(The one with the drain lever) and pull out the tub stopper. You now have a clear shot at the trap. The way you were going in through the drain it ran you square into a tee that you can't get around. Now feed the cable( 1/4" best or 3/3" with a small tip. You can rent a Ridgid K50 sink cable.) About 2' down you will run into the bend of the trap. Crank and push at the same time to work around it. Your blockage will be found in the lateral pipe going to the stack. Good luck and thank you for rating my answer.

What your tenant did when he plunged the toilet is move the clog outta the toilet and on further down the line where it's now backing up outta your tub. You have several options here.
You can snake the drain from the lavatory roof drain. Put out enough cable to reach the base and 16 feet more. **or**
You could remove the tub waste and snake from there.,(see image) Unscrew and remove the overflow plate,(The one with the drain lever) and pull out the tub stopper. You now have a clear shot at the trap. The way you were going in through the drain it ran you square into a tee that you can't get around. Now feed the cable( 1/4" best or 3/3" with a small tip. You can rent a Ridgid K50 sink cable.) About 2' down you will run into the bend of the trap. Crank and push at the same time to work around it. Your blockage will be found in the lateral pipe going to the stack. Good luck and thank you for rating my answer.

But would that cause that to overflow in both sides cause that is what is happening both down stair tubs in both side are overflowing

Batkisson: Both tubs overflow because they share same drain pipe which is now clogged somewhere down the slope. Proceed as Tom suggested to clear the drain blockage.