You'll get the waterfall whenever you drain the coolant and then fill back up. I took someone here's advice about 3 years ago, and it works everytime.
I cut the little 'air bleed' dangle thingy off the thermostat, and then drill the hole out to 4mm. It lets the air purge its self out while you drive for a few days.
I've never had to mess with raising the front end and burping, since this trick.
BUT...if you haven't had the coolant out of the radiator, and the waterfall develops, it is VERY LIKELY a BHG. A tiny leak at the #6 cylinder into the coolant allows combustion gasses to pressurize the cooling system, and gasses into it.
The heater core is the highest postion in the cooling system.