I heard some guys talking about some supposedly commonly available product I
think was called "tuneup" or something similar to that---for outboards in
particular.

I take it that it's used when you get water to the engine through the fuel
line (which I think I did--from an aux tank). And yes, I've already pulled
the strainer, purged the filter, etc. However, I thought i'd try a can or
bottle of whatever the stuff I was hearing about if someone can tell me what
it likely is.