I used a hole saw and used the least amount of pressure on the bit. I also had to use aquarium safe silicone, to seal around the coupling I used. I think they sell bulkheads at most hardware stores though.
Just bought an all metal wing style capper from a guy on craigslist. It is in good shape, already did a dry run with it, however it is stiff as hell. I was wondering if I cleaned it with a solvent and lubed with wd-40 if it would help. I am also wondering if there would be and negative effects...