I usually use a garden hose to flush the rad, block & heater.
Particularly if the heater is mounted high, I remember a Renault 5 we had produced tons of brown sludge out of the heater box but after that the heater worked.
As my drive is on a slope I use that to help the air out instead of a jack.
It is probably worth changing hoses when you do it they ofen seems to fail right after refilling.
