Suction cups ideally hold a hook to suspend and object on a window or flat surface, but many times they do not stick. They work when the air pressure on the outside pushes harder on the cup than the air pressure on the inside. Creating an air-tight seal forms this air pressure differential needed to make the cups stick. To make your suction cups stick better, follow a few tips for their proper use.
Select your surface carefully. Avoid porous, rough-textured surfaces, and opt instead for glass, tile or stainless steel.
Look for the largest suction cup possible to get the best suction against the surface.
Clean the surface and the inside of the suction cup. Wipe up all dust and dirt which prevent an air-tight seal from forming. Use alcohol as a glass and surface cleaner to remove all grease and oils from the surface and from fingerprints.
Wipe all the cleaner off with paper towels to avoid getting fabric fibers on the cleaned surface.
Moisten the inside of the suction cup with water, and press squarely against the surface.
Remove a suction cup by peeling up the sides rather than trying to pull straight from the middle.