I am in the same boat of a new sump. I currently have a 20L DIY sump that I did my self and I am using it on my 75g set up . But when I did water testing then **** of the return pump the drain back into my sump nearly filled up my 20L to the rim . I freaked out that it my flood over the trim. So now I looking at new sumps, and even thought about building my own as well .
If you have room under a 75, you could definately use a 30 gallon tank as a 40 breeder would probably not fit. I have a 30 that I made into a sump and it works great. Check out my tank thread and it explains it.


