“however just remember that it's not really a valid test for filtering pathogens, or for checking for a
cracked filter.”

So First Need and all their engineers and scientists have been wrong all these years?
It appears they have a pretty slick method for finding an internally damaged filter.
From http://www.generalecology.com/first%20need%20original%20instructions.pdf

“A simple test to assure that the canister has not been damaged internally, either during use, transport or backwash is to:
1. Add a couple drops (no more) of ordinary red, green or blue food coloring to a glass of water
2. Pump this solution through the canister.
3. The filtered water should be colorless.
If the filtered water is still colored, even faintly, the internal canister matrix has most likely been damaged and THE CANISTER SHOULD NOT BE RELIED UPON UNDER THIS CONDITION AND MUST BE REPLACED.”

There’s a lot of good stuff at their Q&A: http://www.generalecology.com/qa.htm