Any lubricant that's thin enough to be poured into the bowl will be washed right back out again in just a few flushes...so adding oil or any liquid "head lube" is a never ending job every couple of weeks. Opening up the pump to put a healthy squirt of thick teflon grease into it very spring as part of recommissioning is about 15 minute job--20 if you replace the joker valve too (joker valves should be replaced at LEAST every two years...annually if you live aboard) and will last a whole season for most people without the need to use anything else. So it's your choice...do it once...or do it over and over and over....

Lubrication provides a barrier between surfaces that prevents the friction that causes one or both of those surfaces to deteriorate...in a toilet pump, that would be the inside of the pump housing and the outside edges of the seals, o-rings etc that rub against the housing when the toilet is pumped. The piston ROD doesn't rub against anything...so what would lubricating it accomplish?

Vinegar is a good idea because it dissolves sea water minerals. However use only distilled white vinegar, not cider or wine or rice or any other kind. White vinegar is distilled from alcohol...the others are fermented fruit and veggie juices that aren't nearly as acidic--so don't work nearly as well--and also can leave a residue. A cupful, two at most, of undiluted white vinegar flushed through once a WEEK, not just once a month, when the toilet won't be used again for at least several hours will prevent sea water mineral buildup. Following it with oil kinda defeats the whole purpose.