Why is it that washer fluid reservoirs in your car always hold something like 2-3 quarts, which means that when you refill it with a new bottle, you have a more than half empty bottle to bang around in your trunk?

These things are blow molded, and can easily be made in to irregular shapes, so that they could hold, for example, 5 qt, and then you could toss the bottle after you filled the tank.

It’s kind of like hot dogs coming in packages of 10, and hot dog buns coming in packages of 8.