I have asked this before and have crawled under this thing front to back where the :@# is the drain for the fresh water tank? been using the pump to fill the grey tank and draining that way, I really think there is no drain. any help would be appreciated.
The location to the fresh water drain is in different locations and your 2003 is unknown to me but all I can suggest is the following.
The drain is usually located near the water pump itself and sticks down out of the compartmentunder the rig. Some have found their drain in the area where the propane tank compartment. Mine is located below the access door to the fresh water holding tank and pump compartment.
The drain is a hose with a screwed in plug at the end.
You may also find a fresh water over flow hose with a screen taped over it if you ever over fill.
Maybe that is a great way to find it. Fill up your fresh water tank until the tank is full and your overflow hose should leak all excess water out under the motorhome someplace.
The only other solution if you find someone with the exact same year and model.
We have a 2004 329ds so there is at least some chance ours is similar. Our water tank is over the propane tank, accessible by the same door. The tank drain and the low point drains are located at the back side of the hatch, just ahead if the tires. They have caps as Iggy descibes.