Matt's idea for the car wash is a top tip to get barrels, cleaning them out is easy, just half fill with tap water and put on lid and shake well, do the same three times, then get pure water and rise out using this, barrel now clean and ready for use. if you are really tight with pure water you could use one barrel to wash out about 6, the 005/6 left in will be watered down (pun intended).
One tip I have to give on barrels from the car wash, most are corrosive liquids inside, and it can burn your skin and crack your hands,
so protection and care should be used when washing out
