Not to big but not to small of a hole for a waterfall?

OKay its a 400g rubbermaid and connected to a 6000 gph pump. am having the water come out by a waterfall effect. But how big of a hole do i need? i want it just enough for the water to fill to the top of of the rubbermaid but enough to come out so it does not overflow out. and also for this protein skimmer be able to run smoothly. http://www.proteinskimmer.com/Product Pages/EV1000.htm also about the pump for the protein skimmer it reccomends some pumps but i do not really like the brands they reccomend (to pricey mostly the reason) anyone have pumps you reccomend for it? (i think i should post this question in the sw fourm) how many ghp pump does it need is what am trying to get at. Am trying to make this as simple as possible everytime i try to complicate things i always have a mess on my hands....

thanks

is there a formula ?

for the waterfall? checking now.

i think am blind cause i did not find a sticky on this only on gph pump for a tank you need

anyone?????

http://www.monsterfishkeepers.com/forums/showthread.php?t=400899 update; the skimmer will have a 1500 gph pump (most likely) this will be in the rubbermaid. so again i need to find out a hole big enough to fill the rubber maid (almost to the top not to the tippy top tho) and have the water come out.