When two people get close enough in a scissor like position to connect urethra to urethra forming one single unit. Some have even been known to swap the contents of their bladders.
Steve: "Tom what are those lesbians doing overthrew?:

Tom: "thats a yoga pose called the backwash chimney, we should try it sometime."
by Bryan Leroy September 29, 2021
Get the backwash chimney mug.