Before back-flushing the filter, make sure to raise the water level in the barrel.
Fill the barrel almost to the top before proceeding with the back-flushing process.
Remember not to allow the water level to drop below the top suction hole. Now, you can follow the instructions outlined below.
Important note:
When the red catch has been released, ensure it stays up when twisting & closing
Over-twisting or pushing hard against this catch if it falls, may cause it to snap.