Yes warm the engine, not hot but warm, allow the system to build up pressure, then drop the guts through bottom rad hose... That obviously wont get all the old stuff out but alot will come out

I theory you chouldnt put really cold water into the header tank as it will cause an immediate contraction of the block/head, which isnt ideal... if you plan to flush it through with fresh water it may be a good idea to use boiling / hot water, then again get car warmed up, drop all the water out bottom rad hose,

Ideally have the front of the car higher than the back and as it warms up there is an 8mm bolt in the top of the therm housing, undo this a little and you will see water trickle down the side of it.. thats it just do it up again