This is the drain plug / pet cock assembly from the bottom of the bowl. Use a wrench on the nut closest to the polycarbonate bowl to back it out, righty tighty, lefty loosey. The nut closest to the hose barb is the nut that opens and closes this petcock and is not the one used to back the assembly out of the bowl. Once it is out you can clean it and then replace the gasket and o-ring with the new ones.