Well, the Haynes and Lexus shop manual specify a procedure using a small air purge bolt with a hole in it up near the throttle body where the discharge hose meets up. However, I didn't have too much luck with that procedure.
What I did was put in 2 new hoses in between the radiator core and the engine and then in between the hoses, a t-fitting for a back flush system. Then I disconnected the engine input (bottom fat hose) hose from the radiator. I hooked up a garden hose to the t-fitting, warmed up the car so the thermostat would be open, and then opened the water valve on my house and blasted water through. Oh the crap that came out of the engine input hose! Once the crap was all clear, I hooked up the input hose and continued to backflush out the radiator. This is an important step because you don't want to clog up your radiator and heater core with crap from the engine initially. There could be big clogging chunks of corrosion and other goodies. In hindsight, it may be even wiser to remove the thermostat for the first step (in case of REALLY BIG chunks, and then reinstalll it for the radiator clearing step. However, the current method worked fine for me.
After the radiator was cleaned out, I drained some water out from the drain plug, and topped off with antifreeze, recapped, and filled the overflow reservoir with antifreeze. Abracadabra, all arteries were clear!