sump advice

Hi all, so smy 525XL that I am attempting to give a good clean out to is going well in the actual tank itself, not so underneath as yet, but I thought before I get to far ahead, I should just check for any leaks. So I filled the overflow box in my 525xl tank to see if no 1.) the 3 pipes that are...

What would I have to change to use a sump instead of a Fluval fx6 and Fluval 407? Display tank is 125 gallons, I want the sump tank to be 55 gallons. Any advice on setting up a divider/baffle free sump tank? Can I successfully set up a sump for less than what a Fluval fx6 costs if I already have...