Finally figured out why my bathroom was always musty

I went through a similar nightmare with our guest bathroom for about three years. I was convinced it was a failing wax ring becasue the smell woud get worse every time someone used the shower and steamed up the room. I replaced that seal twice using those extra-thick Fluidmaster kits, but the damp, earthy scent always came back within a week.

In my case, it wasn't just the overflow tube, though that was definatly part of the grime. The real kicker was the condensation forming on the outside of the tank during the humid summer months. It was dripping down the back and soaking into the wood trim behind the base. I ended up getting a long bottle brush—the kind you use for reusable straws—and scrubbing the inside of that tube with some diluted OxiClean.

Combining that deep clean with a small dehumidifier tucked behind the door finally did the trick. It’s wild how much those tiny hidden spots can affect the whole room's atmosphere. I almost pulled up the porcelain floor tiles because I thougt I had a subfloor rot issue. Glad I didn't spend the three grand a contractor quoted me for a "discovery" tear-out.

I had a nearly identical smell in our master bath that drove me nuts for two summers. I was scrubbing the toilet tank with bleach weekly and even changed the flapper thinking the rubber was rotting. The scent was like wet gym clothes mixed with old basement. It actualy turned out to be the overflow hole in the porcelain sink, not the toilet at all. If you look at that little cutout near the rim, it's a dark, damp tunnel that never gets flushed with soapy water. I took a flexible nylon brush and some Tilex and the gunk that came out was unbelievable—black slime that had clearly been colonizing there for years.

I also found that the P-trap under the sink had a slow build-up of hair and soap scum that wasn't quite clogging the drain but was holding onto moisture. A quick zip with a Zip-It tool and a rinse with some hot water and vinegar finally cleared the air. Sometimes the "phantom" smell is just hiding in the one spot the water doesn't regularly reach.

Oh my gosh, I am so relieved to find this thread!! I just moved into a place with a Toto too and I was literally sniffing the floor tiles yesterday like a crazy person trying to find that exact same funk! I'm totally trying the citric acid trick tonight.

Since you mentioned the Listerine—does it matter if it's the minty kind or the citrus one? I don't want my bathroom smelling like a giant piece of gum forever, but honestly, anything is better than that mildew!!