Thats the bottom of the tub, it's the drain. The metal hose connected to the drain goes to the overflow.
My question is more about the flex hose, The threaded end connects to the drain of the tub. How do I connect the flex hose from the drain to the abs plumbing? Is there a fitting for that like a dishwasher nipple?
I see now.
I would say to see if you can find a threaded ABS fitting that will screw onto the drain and eliminate the flex hose. That flexible stuff looks a little too hokey to me. It seems to be designed so that you don't have to redo any of your current plumbing. I've seen some before kind of like that and they were standard 1-1/2" threads, so a 1-1/2" female - ABS adapter screwed right onto it. Be careful not to overtighten or you will crack it.