Where is the petcock for draining the radiator? on 1999 Buick Century

Coolant light comes on quite often but the radiator is full. Also the radiator has slime around the neck. I thought i WOULD TRY and do a flush and see it that helps. The car never runs hot.

Asked by for the 1999 Buick Century
some rad don't have pitcock but it would be on either lower corner. try ck 'ing the rad level sensor, they go bad often or get alot of sludge on them and don't read correctly