if you have an airpocket at the top of the heater core it wont escape it can just sit at the top while the water runs through as the top of the core isnt really low. its like having a bottle of water and trying to fill it from the bottom while water is escaping from another hole...i dunno!? i just hope it works.lol.
i think its better doing it on ramps as 1 guy said he had a really high drive....unless you go half way up the ramp so the back end stays on the flat bit
also worth a quick mention is people swapping over their inlet/outlet pipes.....it backflushes the core with just the right amount of pressure..and very hot water.....then a drain/flush after....it shouldnt affect the car as it water will still be circulating same as before.
im gonna try it on mine and the tilt bleeding. fingers crossed.
if not im just gonna do an A-Z fix of the things that control the heat. ...ie control unit, sensors, mixer blen flaps...and core. a very big bill indeed i just have the feeling it wont be fixed after.haha.