I think the 4oz in 50 gallon assumes you are still using 50oz of Green Wash, which has the scent in it already, so you're boosting it. Just use a really small amount, no real need for an exact measurement. I used a "really small bit" in a 2 gallon sprayer and it was fine, it was probably a half ounce or so. You could probably get away with less. If you have access to a syringe, that would be the easiest way to not overdo it. Probably what I'll do next time so as not to waste. 1oz is equal to about 30mL.