I'm assuming he means the 3/4" original Eheim Male Pipe Adapter with O-Ring Seal on it. This piece fits on the suction end of the Eheim (side). You can pick one up at Home Depot or Lowe's and get an O-Ring, but make sure to get some kind of leak-proof tape, or sealant like plumber's Epoxy just in case you have to make a better seal.
Or you can buy one from Cooltechnica here:
http://www.cooltechnica.com/Merchant...ategory_Code=H