The pipe rubber or stem rubber is a specially shaped gasket fitted to the end of the siphon pipe. Its function is to prevent the escape of carbon dioxide gas from the siphon at the junction of the siphon neck and head.
If it becomes worn or old, water may leak at the connection between the head and the flask, or the pressure in the flask may be reduced, so that not all the soda water can be extracted.
Replacement is recommended during maintenance. It is advisable to apply a thin coat of silicone grease to the junction of the pipe rubber and the siphon pipe.
