brake piston retraction tool

[Bryan Foster]

Listers,
What tool do you use to retract the rear caliper piston when changing
pads?  Where do you buy such a tool?

Does turning it clockwise alone retract it or do you have to apply
pressure?  How many revolutions does it take to get it in?  I tried to
spin it about 10 revolutions with a pair of needle nose but it didn't seem
to be moving much.

Thanks for any advice.
-Bryan Foster