Back-Flush the Straw to Save a Half-Used Can of Spray Foam

The Problem

Expanding foam has a reputation as a single-use product: use a third of the can, set it down, and by the next weekend the straw is a solid plug and the can goes in the trash. Most of what you paid for gets thrown away as a matter of routine.

The Technique

These plumbers-turned-home-improvement pros keep partial cans alive by clearing the straw with the can's own pressure:

1. When you finish dispensing, wipe the tip of the straw clean before the foam in it sets.
2. Bend the straw around and seat its tip back onto the can's valve stem — looping it back to the same valve you dispense from.
3. Pulse the valve. Propellant now flows backward through the straw, blowing the uncured foam out of it and leaving the straw clear.
4. Store the can. Straw and valve both stay workable for the rest of the project.

The trick is doing it immediately after use — once foam cures in the straw, no amount of back-pressure moves it.