In a nutshell, City Walk is the hub of all travel. Go from any of the hotels to there first.
Then pretend that you are staying at another hotel. Find the water taxi or bus going to that one and get on board.
If the pool you are hopping to has a closed gate, try swiping your room key. If that does not work, go to front desk to get it activated properly. Each pool has an inventory of pool towels for you to use and drop in hamper upon leaving.
FWIW, my teens hopped on their own from CB to PBR and were turned away because they were not with an adult 18+. So they got in three rides on RRR instead, lol.