No one knew exactly when the martini glass first suction-cupped itself to the common room table. Or, for that matter, how so much mold started growing in a half-empty bottle of acidic Coke. But with Junior Parents Weekend only a week away and a roommate’s mom set to visit before then, Kelsey M. Muller ’14 said it became clear that both had to go.

“We were like ‘Oh my God, we need to clean,’” Muller said. So she and a roommate spent last Friday night doing just that, working for several hours to purge, pitch, and organize months of accumulated trash. By the time they finished at midnight, in time to celebrate the roommate’s 21st birthday, the duo had filled roughly six bags of trash from their four-person suite in Mather. They even produced a top 10 list enumerating the grossest items they had uncovered.

To varying degrees, juniors across the College have followed suit this week, hiding unwanted messes and unflattering alcohol containers in advance of their parents’ arrival.

“It’s impeccable,” Muller said of the freshly cleaned common room. “Our shoes are all lined up neatly in a corner in a line.”

“We’re not sure if we should dirty it a little before [our families] come because they might be suspicious that it is too clean,” Muller added.

For many, the annual weekend will be the first time their families have been back on campus since move-in day last fall. And though much of the weekend will be spent in uncomfortable togetherness at Boston hotels, dinners out, and House Master’s receptions, the unavoidable and much-dreaded room tour will set the tenor of the whole visit.

“Usually we clean it pretty regularly, but you know how it gets with midterms week and extracurriculars,” said Madhavi V. S. V. Duvvuri ’14 of Adams House. Usually, she said, her family is understanding of a small mess, but on Parents Weekend, the stakes are higher.

“This is a little bit different. All of our parents are coming, and I think that they expect that this is special and we will clean up for them,” she said.

Ayo A. Matory ’14 said that while her room is relatively tidy, her dad “has very high standards.”

While she always takes care to close drawers and hide any spare beverage bottles, Matory said that last time her father visited her Leverett single, not even scuffs on the floor evaded his eye.

Others preparing for weekend drop-ins said that while their own parents might not mind a mess or the other trappings of collegiate life, they have chosen to clean out of deference to roommates’ parents who have different standards.

“My dad appreciates a very clean room, but there’s just some stuff I have to put away,” said David R. Grieder ’14 of Eliot House. “I have some trophies in my room that my dad would better appreciate not seeing, and my roommate’s parents would really appreciate not seeing.”

—Staff writer Nicholas P. Fandos can be reached at nicholasfandos@college.harvard.edu. Follow him on Twitter @npfandos.