‘08 MB, do most LD’s have a low point drain? Can’t find anything underneath.
The water tank has a drain in the lowest outside compartment under the fridge (for a MB).
Aside from that and the water heater plug, there aren't any low point drains like you might find on other motorhomes.
Most owners use either compressed air (blowout the system, as described in the owner's manual) or add a winterizing kit to replace the water with antifreeze when winter comes.
The Lazy Daze Companion: Winterize (http://lazydazearticles.blogspot.com/search/label/Winterize)
Rich