This tip came up in one of the Family and Consumer Sciences Facebook groups I am part of. I’ve implemented it over the last term and highly recommend it!
I have five plastic drinking cups labeled with a kitchen number. Before a lab, an associate, volunteer, or I put a drop of soap in each cup. When students prepare for their lab they rinse out the cup in their sink, dry it, and return it up front.
An important checkpoint in getting a lab ready is having a sink of hot, soapy water and two dishcloths and dishtowels. Labs can get very busy so it I can just tell by a glance at my try which students have filled their sink and have a drying towel. I save soap in the process, which is an added bonus.