I ran a MAg 18 on my Oceanic 75RR. It had a 1" drain with a 3/4" return. Mag 18 does not pump 1800 gal per hour at a 4.5' lift. The person I sold the tank to still uses the pump, and yes you must run it externally to keep from over heating your tank. If it leaks apply a little of high quality GE silicon to the cover.