Open the Shed

After fumbling with the keys a few minutes, you manage to get the shed open next to the pool.  But instead of seeing neatly arranged toys and equipment, there are dozens of rubber duck inner tubes arranged on the floor of the shed looking up at you.

"Help us!" they quack.  "We are being held prisoner by the evil Poolcheck!  Give us freedom!"

"I'll help you!" you promise.

"What are you?" you ask.

Close the door to the shed.