My ferrets like to get in the bathtub too.  I have a ladder splint (like
EMS uses) that I have fashioned into a ladder for them to climb out.
 
For the one who has no back end control, I take a bathmat with the rubber
backing and drape it over the side of the tub.  They can all grab hold of
this and pull themselves up to the side of the tub.
 
And, a lesson you do NOT want to learn the hard way.  KEEP the toilet LID
closed.  Most ferrets won't be able to get any traction to get out if
they fall in.
 
renee :) &
The Poop-in-the-Corner Gang:
Shadow, Oscar, Sir Walter, Dodger & Maggie Mae
[Posted in FML issue 4101]