Milwaukee Duplex
When a guy stacks two women on top of each other and is able to have vaginal sex with both of them during a threesome. If the guy gives either or both girls a creampie the duplex is said to be occupied, otherwise, it is considered vacant. The girls can be stacked in any manner; front-back, front-front, or back-back and they can face upward or downward.
"I was able to fuck Gina and Brooke in a Milwaukee Duplex. I occupied both of them; I hope they are on the pill!"