Actual Ex-Mormon who attended BYU here: Soaking was never a thing, I have only ever heard about it on the internet or literally in the context of Mormons laughing about non-Mormons believing in Mormons doing such things (yeah, they're meta about it).

What is an actual thing is Mormons getting married super early (for a multitude of reasons, one being the horny). Easily over 70% of the students I knew were married by the time they were seniors in college.