Engine Cleaner Household Hazardous Waste HHW must be dropped off by appointment – click for more info. Never Dump Down the Drain Engine cleaner can contaminate waterways if it’s disposed of improperly. Never dump it in the garbage or down the drain, even it’s unused. Dispose of it with hazardous waste. Clean at the Car Wash Car washes are equipped to handle contaminated water. Bring your vehicle to a self-serve car wash if you’d like to clean the engine.