What size Sump

[Kareen15]

I have a 125gl /w two overflows I need to know whet size tank would make a good wet/dry filter I was thinking a 30g would do

[Akili]

A 30 gallon will be quite fine.

[rickztahone]

I always go as big as I can fit. However, with the space under a 125g, I would say a 40g is good.