Daddy did this a couple of weeks ago.
This does many things:
if you have neighbors that complain about boat noise, it will greatly muffle the engines exhaust,
it will allow you to get the engine up to correct operating temperatures for testing and adjusting,
you can easily replenish the amount of water in the drum by hooking the hose to the spigot/drain.
I'd been using a drum cut in half for years on smaller motors, I just never thought about doing this for the bigger engines.