A book about magical plumbing teenagers?

Back in middle school, around 2016, I read some series of books about two kids, a girl and a boy, who discover that there’s some sort of secret magical stuff happening, but all of it is only accessible through enchanting plumbing equipment in mystical toilet goop.

I remember the boy wielding some sort of plunger, and I’m pretty sure one of the books had him fall into a massive sinkhole of mystic toilet goop and come out the other end with white hair and some sort of magic.