I agree, just like putting a potato up an exhaust pipe.
I am not sure of the exact formula, but my engines that run best always have
exhaust piping that is a bit LARGER in diameter than the connection point at the engine.
Since we are not really "condensing" the moisture (ie using it to refill the boiler as in the full size boats)
what we are doing is allowing the water and goopy oil to collect in a can for later disposal.
Not a good idea to just dump it over the side, makes you look stupid and arrogant, and the people
that run your pond (over here the Parks Department) get "xxxxx" really fast.
So make sure that all the exhaust flows "easily" with a minimum of restriction of flow.
Think of a firehose, not a straw.
Just my 2 cents.
Jim