I used a cheap oil suction hand-pump to create the vacuum needed to suck in new coolant into engine to avoid air and overheating and engine damage. Tested with vacuum gauge.
Tee off right hand side overflow hose = 8mm internal diameter, which is what happened to be the hose size which came with the pump :)
Even without a vac gauge, you should be able to successfully do this, so long as you pump plenty of pumps - around 10 on this one. This vid was made after I did the job successfully, showing draining and vacuum and filling sequence used.
BMW k1200s 2005 fill radiator vacuum coolant drain