Brimare57, there are several things in your question and in the answers you are receiving. First, as to the manual: Unless something has changed, the manual is generic and almost useless as to particulars for your unit. There is no unit-specific manual for your unit.
Second, yes, the little valve is for draining your tank.
Third, yes, the other valve allows you to attach a small hose to it that is long enough to come out from under the trailer and into your antifreeze bottles. I had to go to the hardware store and was lucky enough to get one that fit the valve on the first trip.
Fourth, numerous people have told you not to put antifreeze in your water tank. If you've drained the tank, as you should, there is no need to put AF in it, and if you do it, it will make your water taste funny for a long time.
Finally, do make sure that you've drained the water heater and switched the bypass valves to prevent AF from getting in there before you pump any if it through the water lines. Good luck; it really isn't hard to do and NO, doing it yourself will not void the warranty. Your salesman doesn't know what he's talking about. I would really hesitate to take his advice about anything on your camper!