If you ever haved tried to pass a drug test for work before. If you drink alot of water, and maybe something like diet mt. dew, you can pass many tests even if you are pretty dirty. First test Anderson took he was probably pretty dirty, and even watering up didnt help him. 10 days later, and he was cleaner, he watered up big and passed. Peeing mid stream clear uring passes a ton of tests that you would fail.
Post fight he was dehydrated by a grueling battle, and probably gave them extremely yellow pee, that shows everything you have been doing for months. Same thing happen to diaz. Diaz watered up big, to pass, then post fight was dehydrated and failed for that reason.