Got Bopped In Da Head With A Fryin' Pan

[Surfster]

Ya gotta use da baff tub! The sink is not deep enough to see if the needles will sink. They might go arse down and touch the bottom before you know if they will sink slow. Same for big plugs.
Fill the tub with water then stir in a box of Kosher salt to better simulate bouancy in the ocean. (sand ,green food dye and sea shells are your option).
Close the door and pretend your sick. Keep a glass of water on the sink and when you hear footsteps getting close just trickle it into the crapper. Could even keep a few water soaked toilet paper wads to drop in there while to grunt heavy then sigh!

"plunk,plunk...ahhh"

Or add both at the same time to simulate the flu (Eeww!)
They will then leave you to your science. They won't even be near the door when you try to leave with your plugs!