Used to keep the water level to constant through the cycle. Will require a pressure reducing valve as mains pressure is too high for these small valves. You can adjust the length of the arm by cutting and tapping the arm. The arm’s angle is also adjustable to fit your design. Includes nut and rubber washer.
For more information, please read my article on building a steriliser barrel.
https://archersmushrooms.co.uk/how-to-build-a-drum-steriliser-for-mushroom-growing/