Pink foam in radiator

First, the trans cooler runs through the radiator. Make sure there is no internal leak in the radiator which would allow ATF to mix with the coolant. Coolant can get into the trans and it will distroy it.

As far as cleaning it out, chances are it is in the engine too. I recommend draining all coolant remove the lower radiator hose and flush the radiator with a good flush kit you can get at any parts store. Also, remove the thermostat and flush the engine block out through the upper radiator hose. You may want to flush the heater core at the same time.