The windshield washer bag
Back before we had translucent plastic reservoirs for windshield washers, they were plastic bags. At least as I remember, [in many years] they were yellow and, at least in the circles I traveled in, we called them douche bags. The bag hung on a simple sheet metal bracket and was removable for easy refilling.
The washer bags didn't leak at all. The removable cap held the tube in a sealed assembly. The top attached to the bag with a twist, as in the radiator cap.
I grieved when we went to the hard containers but I must admit they hold at least twice as much fluid as the bags. Also, if you skimp on alcohol in the Fall and get caught be a freeze, the flexible bag is probably safer than the hard (read brittle?) container. And the bag was certainly easier to find a place for. Some of the shapes they give us with the hard ones are truly funny!