Most owners manuals are going to be generic in nature and will probably cover the whole range of models within the series. And, probably will not indicate where the drains are.
What your looking for will be, usually, 3 lines that will be comming stright down from the floor. Sometimes colored, red white blue. They will be the drains for the cold water line, hot water line, and fresh water tank. They may or may not have a push on or screw on cap. If you can follow the lines up into the body, somewhere in the line you may or may not find a cutoff valve/lever that opens the line to drain water. The caps, if there, are just that, a cap. The valve itself would be/should be somewhere inside the coach.
You'll just have to get under and search.
Can't be more helpful as each manufacturer places them in different locations....no standardisation. The fresh water tank drain should be somewhere very near the tank itself, and exiting under the coach.
Hope it helps a bit.
Grumpy