10 gallon tank for sump for 55gallon tank

I have a 55 saltwater gallon tank and a ten gallon tank that I used for freshwater and was wondering what is the best way to turn it into a sump for my 55 gallon. The 55 gallon is already set up. Is there an inexpensive way to do this? I have read that an overflow box with a siphon might not be a good idea is it possible to put a pump on it to prevent it from flooding?