Gargling tub

I recently replaced a old lead trap with PVC pipe. There are two drains hooked up to it one from sink one from bath tub. when I use the sink the bath tub gargles. How could I re do this to stop that problem. Right is sink left is tub.

 

You can't have 2 fixtures like that on one trap.

 

All sorts of wrong with that. Cant have 2 fixtures drain to one trap also for hahas tgst 90 is the wrong type....
Need to repipe each drain with a p trap and vent it correctly

 

What would be a better solution then?

 

Since the sink has a p trap under does it have to go through another?

 

No you cant double trap a fixture

 

Every fixture must have a p trap and a vent

If there are any of the P-trap on the sink the most likely it is vented I can't say the same for the tub

 

Can he add a wye just a little left of the p trap shown in the pic?
Then route the drain from the sink into the 45 of the wye, and let the tub trap go straight into it?

There is already a p trap under the sink.

Does he need a long sweep 90 from the sink drain?

Just ideas, not a pro.