I do believe (could be wrong) that if you call winnebago they will send you plumbing and electrical diagrams for your specific camper.
You should have at least 3 tubes sticking out from the bottom. One for the fresh water the other two for hot and cold low point drains. Find those pipes you should find the open/close values. As for the exact location can not help.
Water heater, open up the outside cover so you can see the workings of the water heater. At the top will be a pressure relief valve and at the bottom will be a plug. The plug is a threaded either plastic or brass depending on your heater. I believe it takes a 15/16 or 7/8 socket to remove. You will want to unscrew the plug open a faucet to relieve the pressure and let the heater drain. Now would also be a good time to spray the inside of the heater. Any RV store or even walmart has a wand made for flushing out heater. Per the manual you may or may not have a water heater bypass valve. They did give picture of that being behind the heater itself.
I hope someone with close to your units comes on with more info. as to location.
https://winnebago.com/owners/owner-r...r-manuals/2019
Chapter 7 does explain what to do, but I agree they do not tell you where the items are. Again I would call Winnebago and get the diagrams if possible.