How to clean pulp collector of a fruit juice extractor

The easiest way would be to use an actual juicing machine. Instead of just blending everything together, a juicer will separate the juice from the pulp.

You're looking for something like this:

http://www.amazon.com/Hamilton-Beach-67650-Mouth-Extractor/dp/B000FHQJ6C/ref=sr_1_7?ie=UTF8&qid=1292255706&sr=8-7

Juice goes out one end, pulp out the other.

Some quick research indicates there are enzymes in freshly-squeezed juice that will degrade it fairly rapidly, and that they can be deactivated by heat. Of course, that also changes the flavor (especially since you're not going to be able to quickly heat and cool it, as it apparently only takes 30 seconds, but any method doable in a home kitchen will keep it hot much longer than that). So heat-deactivation is out.

Even commercially-produced (that is, both pasteurized and enzyme-deactivated) juice is only supposed to keep 6 days in the fridge, so that's out.

Your best bet, then, is to freeze it. According to the University of California's Division of Agriculture and Natural Resources Publication 8199, you can freeze in clean glass jars or rigid plastic freeze containers. They also note that navel oranges (and their juice) do not freeze well—they will become bitter.

Well, either that, or store the fruit instead, and only juice it as needed.