Another thing you can do is get an old nipple, cut the nipple portion off and drill a hole through the center about 3/16". Force some clear vinyl tubing over it and screw it into the bolster. The other end of the tubing put in a container of soapy water and start swabbing the bore.
Try a Zerk fitting. It's easier to convert than a nipple, and tube attachment is easier.
http://www.huntingnet.com/forum/blac...lush-tube.html