In the built in overflow there are two holes one that goes into the sump and then one for the return. the tank doesn't come with any of the plumbing so I gotta figure out what piping to use and how to set it up. if you go on craigslist and put in inland empire, type salt water aquarium (seperate the words) its the one that says $300 in moreno valley. theres a pic at the bottom of the ad once you scroll down. thats the setup im getting