Replacement rubber valve seal instructions.
Avid kits were supplied from the factory with Curtis drain valves - one for each wing fuel tank, and one for the aluminum header tank behind the seats.
These valves have a rubber valve seal that will leak and fail over time. It is recommended that the valves be replaced rather than repaired.
It may be tempting to try to install an O-ring in place of the rubber valve seal. This can be a temporary solution to get an airplane home, however it is not to be relied upon.
Replacement rubber valve seals are available. The seal is shaped differently from an O-ring, it is more like a flattened donut. It is difficult to remove the old seal and install a new one without scratching the soft brass valve surfaces.
New valves should be installed with sealant such as EZTurn (FuelLube).