Mary Jo, this is what my vet advised.

Rinse the syringe after each use, when it gets a bit hard to
push/control, draw up some food grade glycerin and empty

That lubricates the inside, and is perfectly safe for the tiny drop
left in the tip.

I found the glycerin in the pharmacy.  You may have to ask for it.

Ardith
[Posted in FML issue 5261]