Leaking joint/pipe. What product to use?
As others have said, fixing this isn't a "get the right stuff to apply to the join" situation, but a "completely redo the join using the correct method" situation. Your plumber did a complete hack job; you risk sewage leaking into your home, as well as backflow into your (I'm guessing) washing machine. And, any sort of caulk you apply will only work temporarily. And, what happens when you want to move the washing machine for service?

If this was done by a "real" plumber, then you should definitely get them back to do it right.

(I don't have the chops to recommend a full fix; perhaps someone else will add an answer that does.)