A kids book from 1972 proposed something similar, deliver packages by weighting them for neutral buoyancy and pumping them down pipelines[0].<p>[0]<a href="http://2010book.tumblr.com/post/324091567/the-restaurant-kitchen-serves-thousands-of-people" rel="nofollow">http://2010book.tumblr.com/post/324091567/the-restaurant-kit...</a>