A Zerk fitting (available from most hardware stores and all auto parts stores) and a piece of vinyl tubing (availabe in any hardware store) can be use to make a useful flush tube for muzzleloaders.

Zerks are available in all of the common threads used for standard and metric nipples.



Just drill through the center, which contains a ball and small spring.



And attach some tubing with a suitable inside diameter



Screw the unit in the nipple seat.



And flush away.