I cleaned out my water tank in preparation for a trip. I notice that there
are two ways to fill the tank. The left side (front)  inlet by a garden
hose, and the right (rear) inlet for which you need the little plastic key
to open.

Both seem to go into the same tank. Is this correct?

My second question is: How does one know when the tank is full? And is it
possible to over fill and over flow the tank? I notice a little breather
hole in the top of the tank. Can one overfill and cause water to flow out of
this "breather hole?"

Thirdly: The cap on the bottom of the sink drain hole below the vehicle is
missing. Is this a regular 3/4 pipe thread? How does one replace this cap?

William Polowniak
1989 Vanagon GL
1988 Mercedes 300 SE