The nut is actually built into a flange underneath the deck. The flange goes on loosely, then you screw the deck drain into the elbow, if the hose is already attached to the elbow, which is the easiest way to get the hose on. But, you have to have the length just right to get the drain to screw into the elbow. You then tighten up the flange nut.
Or, you can screw the flange nut up
tight, then screw the elbow onto the threads below the nut, and then attach the hose, if you have that much room to work with. Put some pipe seal on the male threads and all you need is good hand tight. Mine were not even that, before I removed them, but that connection is not going anywhere.
I had a small piece of flat bar stock, which fit into the grooves in the drain, and used a crescent wrench to turn.
