Animation of two sided sheet runs for 12 seconds. Stop animation at 5 second point. It becomes very apparent that the Klein bottle has an inside and outside but only 1 surface. A Mobius surface?
Liquid is held in by the funnel inlet and the fat "bottom". Seal for filling is the penetration of the funnel neck into the fat bottom. A single surface having volume and inlet/outlet opening...Amazing.

CAPTCHA
This question is for testing whether you are a human visitor and to prevent automated spam submissions.