Every once in a while, I want to run my 40 Merc OB to test it and look for
leaks, adjust carbs, etc, without taking it to the lake and doing it
dockside or bouncing around out there, and perhaps getting towed in.

I have a 55 gallon plastic barrel with the top out. I can fill it to the
water mark on the engine, the same as if it were in the lake. Is this an
advisable way to work on an engine. I have even shifted it into gears, just
not hit the gas. Duh .......

Is it the same as doing it at the lake?

Steve