ok i know theres been threads but i want to know the best way (theres so many different answeres to this all over this site) to flush my block

ive got a brand new radiator and dont wanna start its life with a dirty block (not that my coolant comes out yuk or anything)

but ye whats the best most effective way to flush my block/heating core

Ill be doing it as soon as i get home so my thermostat will be open but i dont really wanna be pulling it out for this task (i have a s1)