Dyeing yarn on a PVC niddy-noddy is a nice way to get regular gradations in the skein. But... regular PVC pipe will bend under heat, such as the heat used in a dye pot (... the voice of experience, sigh ...). Rigid CPVC pipe is needed to handle the high temperature without warping your niddy-noddy.
So, you will need to make your own CPVC niddy-noddy from high temperature CPVC. This comes in about 1" diameter pipe and in T-joints (yay!), so you can get pipe and 2 T-joints and make your own CPVC niddy. The T-joints will add about two inches to the overal niddy-noddy length, so cut the pipe for the center arm about 2 inches shorter than you want your niddy size to be. The pipe is fairly easy to cut with a rigid saw - if you don't already have one, ask for that at the hardware store too.If it helps you find it at the plumbing pipe section of your hardware store -- CPVC is typically beige, while PVC comes in a variety of colors, usually white and black, but also beige and designer colors.
For example, to wind a 4' skein (fairly standard full-bobbin skein size), you would cut your center arm to be 10 inches. Since you are making your own CPVC niddy, though, you could cut it to a useful size for dyeing, such as one that winds a 60 inch skein -- terrific for sock yarn patterning!
I simply "pressure fit" my pipe pieces into the T-joints, they seem to stay fit reasonably well; you could plastic-cement the winding-arms into the T-joint, but not the center arm -- because it's very handy to be able to flatten your niddy for storage.
(based on a post by me on dyehappy, 23May07)