If you just spin the water pump a little bit when it doesn't have water
coming into it, it will be dry enough. Most people don't even do that. I
would be worried about introducing some kind of chemical that might
attack the impeller or the seals. Of course if you run the pump without
water for more than 10 seconds you run the risk of melting the impeller.
Run it too much longer than that and you can fry the engine.
Always change the oil in the fall. If you put it to bed with the old oil
in it, all of the salts, acids and other yucky stuff you have
accumulated all summer gets to work on the engine all winter. Not good.
Some folks change the oil filters every other time, as I believe the
manual recommends. I do it every time.
Also some folks change the plugs in the spring after the fogging oil and
fuel stabilizer is all burned up. I do them every other year. I also
change impellers every other year.
jeff >> Stay informed about: Winterizing a Honda outboard 4 stroke (90HP)