Ensuring your propane grill is in good shape before a cookout includes checking the propane tank to determine if it needs a refill. The easiest way to do that is to use hot water.

Simply drizzle a glass of hot water over the tank and run your hand along the metal. You'll feel a cool spot where the propane level starts, and the area above it will feel warm.

The line where the cool and warm areas intersect shows you exactly how full your tank is. If this line tells you that the tank only has about 20% left, it's high time for a refill.

This trick works because the propane will absorb heat from the hot water, cooling the tank’s surface, while areas of the tank with no gas and only air and vapor remain warm.