getting latex to vertically align all text blocks on a page instead of vertically justifying them

Question

I'm typesetting a book (documentclass = book) and every page compiles so that the first line is aligned with the top of the latex page and the last line is aligned with the bottom of the page - but this means that there's variable whitespace between paragraphs.

Is there a parameter I can change to force latex to not change the whitespace between paragraphs (I don't mind having differently positioned last lines on every page even though this is usually typographically verboten)? There is a suggestion elsewhere on Stackoverflow to try removing the rubber from /parskip but this doesn't work (the whitespace is still variable).

I am trying to figure out how to include an MWE that isn't the entire book; will update. If anyone has any thoughts in the meantime, I'd be much obliged.