Because it's essentially a hole in the ground that it lined with rocks, drainage can be an issue. I didn't want to deal with the problem of it filling up when it rains and having to wait for it to dry out, so I built in drainage.
The pit is located at the top of a natural slope, so I simply dug a drainage ditch & placed my homemade pipe inside. I had fashioned it out of steel cans (in this case, formula cans) with their bottoms cut out. I simply lined them up & duct taped them together. Yes, I know how cliche that is, but it worked well to make sure that none of the cans moved while I built the walls of the pit or covered the pipe.
As you can see, I placed rocks at the opening of the drainage pipe to prevent erosion and covered it with soil & transplanted grass. Clearly part of it is still visible. However, I plan to wait until the grass has the chance to get a firm root before I disturb it further. At that time, I plan to cover more of the can so that it is almost entirely camouflaged. Overall, this was a relatively easy project that took only a couple hours, but I am happy with the results.