DIAGNOSIS The GTW465ASNWW does not have a dedicated "Clean Washer" button. The cleaning cycle is initiated through a specific combination of settings.
FIX Ensure the washer is empty. Add 1 cup of liquid bleach to the bleach dispenser. Do not add detergent. Turn the cycle selector knob to "Normal". Press the "Temperature" button until "Hot/Hot" is selected. Press the "Soil Level" button until "Heavy" is selected. Close the lid and press "Start/Pause". The washer will run a prolonged, hot wash and spin cycle to clean the tub.
IF THAT DIDN'T WORK For removing hard water scale and detergent residue, use a washing machine cleaner like Affresh instead of bleach. Place one tablet in the empty basket, not the dispenser. Run the same "Normal", "Hot/Hot", "Heavy" cycle.
HEADS UP Regularly wipe dry the door gasket (boot) after cycles to prevent mold. Leave the lid open between washes to allow the tub to dry. Run this clean cycle every 30 washes or once a month.