Knock on the hatch.
The knock speeds up.
Someone who pointlessly knocks on the door.
Aaaand you're not allowed in my house anymore.
So they can stand closer to the sink
StockHOLMES!
Artifical Swedeners
Swim down and knock on the hatch. (In Sweden we have a running tradition of telling jokes about stupid norwegians. They do the same about swedes)
Bless you!