I expect you mean you used Glyphosate. The instructions probably say wash out three times. Put it in the kitchen sink, wash out once with water, then refill with warm water and a drop of WUL, pump it up and let it squirt out through the sprayer, then when empty, a plain water rinse. Like homeopathic medicines, there is so little of the chemical remaining that it has no effect.
BTW, for fertilisers, a watering can is the usual method. You want them to be very dilute.
Keen gardeners buy a red watering can for weedkiller, and use a green one for everything else.
There are special hormone weedkillers for use on lawns, and they are very persistent, causing stunted and distorted growth on some other plants, especially tomatoes.
