Whats the best way to patch holes drilled in the bottom of a tank?

[ScubaSteve]

Personally, I'd leave it as is. If you spend some time tuning the system and getting the plumbing inside the overflow box right (herbie overflow), it should be nice and quiet.

[sphelps]

Yeah coast to coast won't be any quieter unless you're planning a wave box or something else that will generate an actual wave but such devices are noisy alone. Standard box with a herbie will be completely silent. Sounds like you've already got two holes so you're good to go.