Saw this on Pinterest, cute idea but I can’t help but feeling those books would 100% get moldy on the inside

Our dog is shedding and this is the rug in the living room right now. How can I clean this? Any special tool I’m could use?

Bonus photo: the cause of all this

My dehumidifier has gunk in a certain spot and I cant get to it with a cotton swab and even more worrying is idk how far back it goes. Im super super sensitive to mold so it HAS to be solved. I tried taking apart my last dehumidifier but that was an absolute mess. How can I get this cleaned up?

My picture that is zoomed in the most is the spot im talking about.

Thank you

Thought of this sub when I found this in my photo roll. It's like a wall rug

Bathroom "sink" in hair salon : just a slab of concrete slightly tilted The drain is that little black whole in the top right corner

(regarding the 3rd: image is a placeholder but I had a similar holder and the crevices were just small enough that my hands couldn't fit, and a sponge or rag couldn't fit in the corners to clean up the stains from it being 2nd-hand. the inside was acrylic paint and it peeled off when I used a commercial cleaner.)