On the VT VX #drain... have the heater set to high run the motor for a min and then get a suitable bucket place under lower radiator hose, undo the lower radiator hose.
#flush take off the in and out heater hoses and with the garden hose or if possible pressurized soft water flush the heater box until it runs clear then remove top radiator hose and stick hose in lower opening and back flush the radiator, then if need be flush the block, then refit everything. and add red coolant (better for alloy blocks) mixed with soft water which include rain water, De-mineralized water and distilled water. The LS1 will self purge the air out when in park hold at 1.8k for a couple of mins with the overflow tank lid off.