Freshwater tank leaking from drain valve

I think Old-biscuit's method will be the best fix for me. ID is 1/2" and OD is 5/8" - that should help me get the right size fitting narrowed down. I may even insert an elbow and then route it out towards the frame a little and then install the valve so that it is better protected. Good idea? Bad idea? I figure as long as it angles downward it should still drain well. Here's what I'm dealing with:

Here's the assembly removed



Here's the assembly all taken apart



Here's the drain tube coming out from below the tank