I don't know who Jim Humble is...but I went to Naturopathic Medical school, and I am currently on Day 4 of a water only fast...including an enema every morning upon waking.
NEVER EVEN THINK ABOUT USING A CATHETER ANY LONGER THAN 2.5 INCHES!!!
The rectum (the STRAIGHT, final portion of the intestines is itself only 4 inches. Then the rectum turns "S" shaped (Sigmoid colon curved like an "S").
You don't want to accidentally jab, injure, or stab the sigmoid portion of your intestine (which, again, begins 3-4 inches up from your anus) by using a catheter longer than 2-3 inches MAXIMUM. SERIOUSLY.
This is the most important advice I've probably ever given in my life!
As for as equipment. The other poster gave you excellent advice about using a 2 quart stainless steel bucket type of water container. Then hook it up to clear surgical grade tubing, with a basic 2" plastic catheter tip, and simple water cut-off clip...and that's it. The stainless bucket is most sanitary, convenient to use, easiest to clean, and lasts a lifetime.