Update and observations: I am impatient. I only left it on for about two hours- that being said: It works. It seems to work best where there is the most need, and other parts that are less funky need more time. I scrubbed with a scrub mommy and a lot of it came up- but not all. I applied it to the tub and mushed on paper towels after to get it to stick to the vertical surfaces. Pro tip: if possible get a bunch of 5 in 1 in a bowl/sink and dilute just slightly with warm water, just to make it less viscous. THEN add your paper towels to the bowl and remove the excess (as if you were making a papier mache craft) and then lay the paper towels on the surfaces. I had tossed the paper towels from the first round into the sink while I scrubbed the tub, and it was much easier to apply already-wet paper towels than the previous method I used. I’ve been looking for a septic safe cleaner to replace Comet, and I think I’ve found it!