help with sump and protien skimmer

[Nano]

Hi guys any of you following or helping me in my threads will know I have a 20g reef with a 20g sump and no skimmer. So here's my problem.. I got my sump used and its been running for almost 3 months it doesn't work well cause it was not made properly, and lastnight it began to leak. So I have a 20 gallon I have had tucked away for emergencies, luckily and I would like to make it into a sump and fit a small protein skimmer into it.. only thing is I don't have a clue what to do. I know I can make obvs overflows that don't require drilling, that's not problem, I just don't know how to set up a sump.