Drilling tanks and have questions

[Beanz]

I have some questions about drilling tanks. I am wondering what kind of overflow would be best for the 15 gallon tank i have and the 45 i have. What size of holes would provide enough gph for these tanks. I am thinking of doing beananimal overflows for both tanks because they are in my bedroom and would like the overflows to be quiet. Would this be ok for such small tanks? I haven't seen them done on small tanks really. Also how close can you drill the holes together and how far should the be from the edges/sides of the tank?