flushing a heater core

reason I suggested that was a friend had put black pepper in radiator of his welding truck to stop leak but when winter came his heater wouldnot work so swapped hoses and heater started back working. I put some liquid glass in radiator not long ago and stopped it up so I used a trick I learned from running heavy equipment and put Tide detergent and it cleaned it right out. I used the liquid for my front loading washer that doesn't suds as much