I emptied the waste toner and the red light is still on....samusng clp-300 which says that it is full

Sometimes just emptying the waste toner tank will not clear this fault. The printer uses a light sensor to determine when the tank is full. You will need a cotton swab and clean the part of the tank that the sensor is viewing the tank. Try to clean the clear window of the inside of the tank. It can be difficult since the placement of the window with respect to the tank opening. Other way is to try to wash out the inside of the tank with soap and water which can be messy but it will do a better job. Hope this helps.