With all due respect for Vasiline advocates, the stuff will eventually damage the lips in the lip seal at the top of the pump. If the pump is becoming difficut the rod can be lubed with a non-petrolieum based lubricant, e.g. a silicon grease lube.
Frequently, stiffness in the pump is a combination of the stiffening of the O-ring around the edge of the piston coupled with build-up of scale in the discharge hose directly aft of the Joker-valve. Adding a lubricant to the bowel, pulling it into the cyclinder with one or two strokes and then leaving the piston in the up position over night will lube the cyclinder and allow the piston O-ring to recover somewhat. Peggy Hall, the gruru of Head Maintenance also suggests pumping a bowel of water thoroughly mixed with a product known as "Salt Away" through the lines and allowed to sit over night. One can also use a product known as "Ryd Lime" (biodegradable) in the same manner or, in extremis, a couple of bowels with a 5% mix of Muriatic Acid although that should only be allowed to sit for 20-30 minutes before being flush out with fresh water (Raritan suggests at least 10 gallons of fresh water).
We keep a squeeze bottle with a solution of water abd Salt Away in both heads and always add a few quirts to the last bit of water in the bowel once the heads have been pumped clear after use and both heads have remained free for several years at a time.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."