A toilet having a one piece structure, a flush valve, and a seal. The structure includes a base having a fluid channel in fluid communication with a bowl; a tank having an internal compartment; a wall disposed between the tank and the base, the wall having an opening fluidly connecting the internal compartment and the fluid channel; and a retaining structure in the internal compartment. The flush valve has a valve body including an inner wall, which is disposed in the opening and extends from a first end in fluid communication with the internal compartment to a second end in fluid communication with the fluid channel, and a locking flange extending radially outward from the inner wall, the locking flange being retained between the retaining structure and the wall in a locking position. The seal is disposed between the locking flange and one of the wall or the retaining structure.