The reason that most trailers tow better with the water tank full is that typically the water tanks are located in front of the axles and thus the extra weight from the water increases the hitch weight. Ideally one wants a hitch weight that is 12 to 15% of the total trailer weight as this results in the best balanced arrangement in terms of forces on the tow vehicle and trailer.

Likewise since most holding tanks are located aft of the wheels, when they are full they reduce some of the tongue weight because of the see-saw type of effect.

Most trailers list ther weights as "dry" weights but are engineered for full water tanks and empty holding tanks. As one begins to deviate from this arrangement, the vehicles begin to react in less than ideal manners.

In my trailer it is a noticable difference when the water tank is even half-way empty. And as far as preferring NOT to drink from ones own fresh water tank seems to me that one is missing much of the self-supporting beauty of the travel trailer. I always love it when I can go somewhere and not have to
hook-up yet do not suffer from want or need of anything in terms of utilities. I always felt that this self-supporting feature of RVs in general, and Airstreams in particular, was one of their most attractive features.

Tom H.