A little more progress. I laid out the holes for the drain and the flood.
Using a hole saw I cut out the holes. The big hole is my drain/fill hole, the small hole by it is the fill/drain, and the one in the corner is the overfill.
I accidentally broke the plastic drilling it, so a nice coat of silicone will solve that problem.
I installed the fill/drain, then cut out the screen and did a dry fit.
Looks like I’ll be able to get a dozen party cups in here. 
