Some people prefer to use non-absorbent cat litter for collecting urine samples.
In this case, you would just replace the usual litter you use (or use a separate litter pan) with the new litter pellets and let your cat use the box as usual. Take your sample and proceed with the test.
Some of our clients use these pellets only when doing ThePetCheckup test and others use them as their regular litter. You can buy the pellets and also a cleverly designed litter box which enables the urine to flow into a collection unit underneath the pellets. Check out http://www.smartcatbox.com for further information.