We have drain pipe (plastic) tunnels too!  The lady who runs the ferret
shelter here in Oregon mentioned it was great.  We first bought it to run
behind the entertainment center, water bed and refrigerator.  It works
great!  No more trying to plug everything back in after Razz or Tazz run
behind the T.V.
 
Now that mine have their own room, we ran the tubing up around the top of
the room with big dips for sliding.  It is easy for them to climb and ours
climb straight up the wall and then you can hear them running around the
room.  Once in a while you hear a SWOOSH as they fling themselves down the
tilted parts (slides).  It is so inexpensive and they love it.
 
We also use it for them to get from one level of their cage to the other.
 
Hope
Razz & Tazz
[Posted in FML issue 1464]