I plan on making a "poo spray" (like this stuff) as gag gifts this year. For those who haven't seen it, it uses the "oil floats on water" idea to block some of the stronger smells in the bathroom. I've made a prototype for myself using water, isopropyl alcohol, canola oil, food coloring (to tell when you have enough coverage) and cinnamon oil in a cheap 8oz sprayer bottlethat has an adjustable sprayer. I also added germaben as a just in case. In the recipes I've researched some people say to use vodka (and mention that as a preservative), one site says to use glycerin, as an emulsifier. It works, as far as I can tell, the issue I'm having is best described as splotchy coverage. Unless I use 15+ sprays it doesn't look like there is even coverage over the bowl and the colorant spreads to the sides. My guess is that the sprayer doesn't have a full coverage spray. The math I'm asking about is for the alternate bottles I want to use. I ordered some bottles with a dropper top that I hope will have more even coverage. For labeling instructions I'm trying to figure out an estimate of how many drops/sprays to use. I plan on using a basic area of a circle but don't know how much coverage a single drop will spread or how thick the layer of oil needs to be. I just check my order status and it won't be delivered until a few days before I leave to visit family. I definitely will not have testing time before I need to make labels and have everything done. Does anyone have any suggestions on how to do the math? Or a basic formula for how far a drop of oil spreads?