After my car broke valves, there is a white and brown sludge/cream in the water tank. Reckon it happened when the car broke, and the metal grindings and oil was pushed into the water tank. I did remove it and used some water and sand to try clean the inside of the tank. It did get a bit cleaner, but still not clean enough as the sludge still sticks to the inside of the tank. Can anyone suggest something that would remove this? Will radiator flush help?