My two cents' worth (or ha'p'orth from under my British hat)
  is based on some work done in my lab about 12 years ago.
  We were collecting 2 cm pieces of large and small intestine
  from dozens of rats & mice (mostly mice) that had been dosed with
  senna and related purgatives. We needed to know the distances of the
  samples from the pylorus (or from the caecum), and also the
  total length of the small or large intestine (Both are both rather
  variable because it stretches. With measured lengths, the position
  of a sample can be identified as a proportion of the whole
  length.)

  To get a straight, measurable, whole GI tract, the simple answer
  was a piece of plastic eavestrough (that's gutter in UK) about
  5 feet (1.5 metres for Young Canadians) long. To use it, put one
  end over a sink and elevate the other end about 6" or 15cm. Lay
  out the intestine along the length of the trough, with the anal
  end over the sink. (Remove the caecum and treat the small
  intestine and colo-rectum as separate, parallel objects.)
  Straighten out any loops & twists and make the length measurements.
  Then inject saline from a 20 ml syringe, downhill into the sink.

  The point I'm trying to make is that a length of plastic gutter
  or eavestrough (mine is still quite brightly white and stands
  in a corner taking up hardly any space) is a great petty-cash
  item (about $5) for any lab that has to handle and clean out the
  intestines of small animals. Imagine what a lab supply company
  might charge for a "fully adjustable oblique-flow intestinal
  irrigation apparatus, customized for small rodents."

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1

  P.S.
  The saline should be followed by fixative if you need well
  preserved villi. Nearly all our material, however, was made
  into  whole-mounts containing the myenteric plexus,
  which was supposedly susceptible to the metabolites of senna.
  If you have read this far and want to know that purgatives do
  very little to mice and their enteric neurons, please email me
  personally and I'll send you a reprint. In addition to the senna
  study, we did neuron counts in wholemounts stained for RNA with
  cuprolinic blue. This method has since been used, by others, for
  larger animals, including cattle.
                                     J.K.