Product review (3 stars): Works fine but is a little tricky
This tube works as advertised, although I found it a little tricky to make a bend as sharp as the original tube. Since my problem was just that I needed a slightly longer tube, this caused problems. I ended up solving it by offsetting the insinkerator slightly, allowing for a shallower bend. Besides that, this worked fine. [Note: see edit!]

As others have noticed, this tube comes with no instructions, and this is the only thread on the web where people are posting solutions. So after having gotten it working, I should probably add some clarifications and corrections to the comments below.

1. The hard white plastic gasket should *not* be used if you have a single- or double-bolt attachment to the insinkerator. Like others below, I spent a long time trying to fit the white and black gaskets together in some fashion, but the white gasket is just an evil trick designed to make you crazy. Breadrunner's review below with the insinkerator email makes it clear: the gasket is designed for the threaded discharged disposers. If you don't have that, just throw it away. If you do have a threaded model... I hope it's clear what to do with it by looking at it.

2. Now that the white gasket is thrown away, the rest is easy. Slip the metal tailpipe flange ove the flange of the tube by first soaking the end of the tube in hot water. The metal flange won't seem very snug, but so long as you didn't damage the tube, it will be fine [Edit: Nope! Use teflon tape. See bottom]. Place the black rubber gasket in the insinkerator with the flat side outwards. The tube will just press against the flat side -- no trying to get the little rubber lip into the tube, it won't go. Bolt the tube to the insinkerator tightly and you're done.

*EDIT*: 2 months later, neighbor downstairs complained that he suddenly started getting dripping water coming from the ceiling. Checked under the insinkerator and one side of the white flanges of the tube had popped out of the metal flange...

I took it apart, slipped the metal flange back on, and wrapped the white plastic flange with many layers of teflon tape, making it significantly thicker and snugger. Bolted it all back up tightly. Fingers crossed, this has worked for me since then. I've downgraded this review down to 3 stars because of the looseness of the white flange.