You can cold flush the system by removing the heater hose at the rear LH side of the head and use a garden host to flush the engine and heater core circuit. You can rig up adapters with plumbing supplies.

Drain the coolant cold, then flush. When changing from green to G-05, I'd also recommend a couple of hot flushes - fill the system with water, start the engine and run it until the thermostat is open for at least five minute, then drain.

Allow about an hour between hot flushes to let the engine cool down.

Duke