Measure to Save on Mouthwash

I used to just pour mouthwash into a bathroom cup without measuring. Now I know I was wasting a lot of Listerine. The recommended amount per use is just 20 milliliters. I noticed the plastic dispenser cup on one of my almost empty cough syrup bottles also used milliliter measurements, and it is clearly marked to aid in dispensing. I now keep that cup on top of the mouthwash to measure the exact amount needed. This is saving me money.