leaking shower

[ldr161]

I have a leaking shower drain. The shower itself is located on the 2nd floor. I cut the drywall and can see the water coming down the abs pipe. there is a large brass nut underneath. It seems tight, should I try to tighten it more or try something else?? The house is about 2 years old and it is a fiberglass shower pan.
Thanks in advance

 

[Jimbo]

Without seeing it, here are some comments: The brass nut holds the drain flange into the shower pan. That area is probably NOT the leak, but if it is, tightening the nut probably won't help. The leak may be around a rubber donut that seals the black pipe. We need pictures!