Just a quick couple of comments. A) Looks like it's very easy to make. You could use a cutting die and a press to make a smooth hole versus cutting one with a knife. Sometimes a cheap exacto blade will do the trick better and not bugger up a good blade. B) NEVER EVER ALLOW CATS around your filter. Many cats have Toxoplasmosis gondii. They spread it to humans because their paws have walked around in a litter box of feces. The guy in the video just contaminated his filter through carelessness. It's a protozoa that's passed in cysts and then recreated in water sources. Not smart at all.
[link to www.vet.cornell.edu]
Possibly 1/3 of cat owners have the illness world-wide.