Bernhard,

When you post the same question on another site, I will not answer in detail. Besides, this expressly violates a rule of MHF. However here's a hint:

How do you get a torus? Answer, for one such torus, rotate the unit circle centered at (2,0) on the x-axis about the y-axis. Write down the parametric equations for the resulting surface and the homeomorphism should be clear.