I always use a metal street elbow at the bottom, and usually a male threaded PVC adapter into that. Never use a female threaded adapter, or it will surely leak at some point. In fact, I never use a plastic female threaded adapter anywhere in a water system. I bury a cinder block vertically under them, as well as no.3 stone, and they always drain down fast.

Also, mine always have a vertical 4x4, or pipe driven into the ground well below the riser, and the hydrant strapped to that. Always leave plenty of room to be able to screw the top off of one-not against a wall. It will need to come off sometime in the future.