This y-piece makes it easy to remove the unwanted oil from the pressure tube of the carburettor. Loop-in the two "branches" into the pressure tube and extend the "trunk" about 6-12 cm to lead it to the lower side of the cowling. Place the y-piece underneath the carburettor and the surplus oil will be gathered into the "drainage tube" and can be dumped from time to time, without removing the cowling.  Attention do not forget to close the tube securely with a plug!