Welcome to the adventure
We have a new to to us 2017 ACE 29.4 and those generic manuals are almost useless. But, if you read enough of it you might start to figure out which sections refer to your rig. The Thor Customer site (
https://thor.mizecx.com/login.html) after setting up with your VIN has a ton of information, again, you have to figure out what applies to your coach. I got lucky and discovered a work colleague who has a 2015 ACE 30.1, which shares some components.
Now to your fresh water drain valve question, I read manuals, forum threads and talked with my buddy and finally found it! In mine it's under a drawer in the bedroom. Had to squeeze my head into there with a headlamp on and found the valves, which I couldn't get to with my head in the hole looking at the valves. So it takes a bit of a contortionist move to get it, but there it is
Good luck and have fun
Remember its a journey!