Back in those days, condoms were made from vulcanized rubber. They were also considered reusable, but because they had a lengthwise seam which often split, they at least had to be replaced semi-occasionally. So, the “throwing it away” part is at least plausible. I don’t know if knot-tying was at all common or if it was even practical (the rubber was over a millimetre thick), but this is the part where my artistic arrogance license allows me to disregard historical fact for the sake of a joke. It probably would have been more effective if I hadn’t launched unprompted into an unnecessary explanation.