There's a how to guide on youtube for bleeding the Bongo and it's in 3 parts of 10 minutes each. Basic idea is you have to attach a large funnel onto the bleed hose and seesaw the water level back and forth between the funnel and the header tank until the thermostat opens and then seesaw some more until no more bubbles appear while revving the engine to force air out of any corners. If any air gets sucked back in at either end then you have to start again and at the end you have to remove the funnel full of boiling water and cap the pipe without letting air in or burning all of the skin off your hands. Some have suggested that this is a poor designHow do you bleed it? I just do what you wrote (empty, flush, fill with water, run for a couple of minutes, empty, flush, then refill with mixture)
then run it and top up.
I always change the thermostat too.