Double-paned windows provide home and property owners with security from outside elements and some degree of protection from breaking and entering. The downside to double windows is that they can be prone to collecting condensation that results in parts of the window fogging up and decreasing visibility. The buildup is a result of aging sealant that breaks down and cracks, which allows moisture to enter. Luckily, there are some remedies to the problem.
Outfit the drill with a glass-working drill bit. These bits, made of tungsten carbide, will allow successful drilling of glass that other metal-based bits cannot do. These bits are typically available at hardware and home improvement stores, but if you can't locate one, a diamond bit will perform the work as well.
Put on your safety gear. Eye goggles and a dust mask will prevent small glass particles from entering your eyes and lungs, and as ear plugs will protect your ears from the loud noise of drilling in enclosed areas. Select a spot on the window to drill a hole; you should drill toward one of the window's four corners that has the highest concentration of condensation.
Drill a hole into the spot you selected. Be slow and precise and don't rush the job or apply too much pressure on the drill or you'll risk splintering the window. Drill completely though the first pane; stopping once you've broken through. Reverse the drill, remove it and place the suction hose over the hole.
Turn on the wet/dry vacuum and allow several minutes for the vacuum to suction out the moisture. You should see the vapor dissipating and the window becoming clearer. Keep vacuuming out the space for a several minutes once the buildup is gone to remove unseen moisture.
Insert the defogging device into the hole; this rather unassuming device seals the hole you drilled and serves to provide ventilation for moisture to escape.