ok think about a fish tank four sides so you need four people 2 girls and 2 guys make the guys face the girls and then they have sex standing up so they make a two lines next to each other like the equels sign. now there are sides air between the people are the sides and a bottom!
man: lets fish tank all night
lady: but we need more people
man: get your roomate i 'll get mine
and they fish tank alllll nite long and moan
I like the wayyy u fish tank baby