I just pulled the cork on the Woodmaster as I drain and refill it every spring. Never much though about what I am draining out of it besides water, 1/2 gallon of whatever "boiler treatment" is. Looks and smells like what I put in the cooling system of my Ford diesels. Anyway it has never killed the grass is all I know abut it. This year we have a new batch of kittens running around here getting into everything and it has me wondering. Jug says nothing about disposal problems, anybody know for sure? hard to keep them kittens contained, LOL.