Yeah, King has some weird sex and sex related stuff in his books.
But truth is that it usually fits. As in the kind of weird the sex is relates to the life kind of weird of the story, and/or is used as something to showcase the overall weirdness of a character.
I say usually because the scene from It only makes sense in context if you really stretch credulity to the breaking point.
The problem is that even when it fits, it tends to be so far over the top that it breaks immersion to some degree or another.
King is one of those authors that you end up having to accept a good degree of stuff that's nigh edgelord absurdity as part and parcel of some very unique and engaging stories. There's also a ton of pseudo-surrealism in his stuff. That usually works great! Even when it's absurd, the absurdity of it works, like the weird lobster things in the dark tower series and their "Dad-a-chum? Dum-a-chum? Ded-a-chek? Did-a-chick" shtick.
He's not the only author to do that kind of thing, but he's one of the few that are successful at his level.
I can't even remember who wrote it because I've mostly blocked out the memory. But there was a book with a chapter long rape scene involving two jr high kids. There was a ton of detail about pink things and a fetishistic attention to the dress the girl wearing. But it was all because the boy was possessed/influenced. Like, that's just lazy writing imo. At least King in the IT scene had an internal reasoning beyond "this is what evil does". It was still batshit crazy, and unnecessary, but at least it wasn't lazy.