This is a sexual position providing 3 males and 1 female. The female stands straight up. The first male has vaginal sex with the female. The second male has anal sex with the female. And the third male has anal sex with the second male. This is simply a lop-sided eiffel tower, hense the name Leaning Tower of Pisa.
"The other night, Chris, Todd, and Josh got drunk and gave Erica the Leaning Tower of Pisa."