Once he was sure no moisture remained (tested by taping a clear bag over the holes—no condensation formed), he injected the low-viscosity silicone into both holes until a tiny bead squeezed out. He then pressed clear mylar tape over each hole. After 24 hours, he shaved the dried silicone flush with a razor blade.

He filled one syringe with alcohol. Through the first hole, he gently injected. Instantly, the white fog swirled like a snow globe. He watched the alcohol run across the inner surfaces, collecting condensation. From the second hole, he used the other syringe to suck out the dirty, now-cloudy liquid. He repeated this—inject, tilt the window to let the alcohol wash all surfaces, suck out—six times until the extracted liquid ran crystal clear.

When the fog finally returned in year four, Mark didn’t sigh. He simply ordered a new IGU, removed the sash, and replaced the glass unit properly—this time with confidence, because he knew exactly how the enemy worked.