I do not think it was in the book, rereading the book again (2nd time), because of the series’ changes, or the 1990 Mini-Series (my opinion best visual expression of ‘It’) & much later 2-movies (I disliked both, but keep giving them a try to impress me & they fail).
I liked the series a lot, even with gory bloody scenes (I hate those type of visual entertainment & never scares me, just grosses me out) & main, Kid, character dying, until the following changes that make no sense.
I hate it.
Was never necessary,