moving bed filter

Hey, so after a bit of a false alarm with my secondhand 120 gallon tank's seals (it's been holding water for a little less than a week with no incident), I'm back to the task of figuring out how I'm going to handle the filtration and plumbing. While it's by no means necessary for a tank of this...

I'm sure there are more people on here that know more then I do and have more experience setting up 55 gallon barrels as a moving bed filter system!!!! Does anyone know what the push in connection things are called where you put a rubber gasket between the barrel and the pvc piping. I'm trying...