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Because my son suffers from respiratory issues, it’s important that we keep his humidifier clean. Although we were changing the filter regularly and keeping the filter tray clean, I noticed a funky yellow substance building up in the bottom of the water tank. The trouble with our particular model was that I couldn’t open up the water tank to effectively clean it.

What didn’t work for us?

I tried all sorts of bendy-necked scrub brushes. They worked…but only as far as they could reach. There were those hard-to-reach areas that stayed coated in a yellow film, and the newly cleaned spots just served to emphasize how gross the dirty spots were.
I tried vinegar and baking soda, which provided me with a fun, explosive mommy playtime in the kitchen. Aaron and the kids ran in after hearing loud pops followed by me whooping hysterically. Maybe the baking soda and vinegar method worked for other people online because their humidifiers weren’t as filthy as mine, but it didn’t make a dent in my yellow scum.
I tried bleach as a final measure. I figured bleach would lay the hammer down and wipe this bad boy clean. I was wrong. It hardly touched the funk.

What finally worked?

Driveway gravel. As a last-ditch effort, I walked out to the driveway, grabbed a handful of gravel, threw it into the water tank, shook it around until all the gunk was gone, and rinsed out the tank. It was noisy, free, simple, quick, and 100% effective.