OK - (embarrassed) - I just discovered where my water heater bypass valve is. Hey - It's not marked and it's hidden behind some plumbing lines!) Since NOTHING is "standard" on RV's....LOL!! I'd offer to pay them a few extra bucks for the additional antifreeze - and have them do a complete system operation including winterizing again. Either bring a camera; or take notes because some of it is going to be a blur....
Our first time camping with our Class C (about 3 months after our PDI), we went with friends who had a Class A - and they happily went over a lot of little things like how to unfold and lock the awning arms, for example.