How to add a compact washer

[Quercifolia]

This photo was taken from the closet access panel. I would like to add a compact washer and have the space for one. You can see the hot and cold lines but I’m wondering the best way to connect into the drain.

 

[breplum]

That tub overflow is not the place. You need a new 2" drain cut in underfloor. You need a plumber.