I removed the thermostat housing in order to change the thermostat & found an awful lot of rust on the front side (where water would sit when the thermostat is closed). The housing needs to be media blasted, cleaned & the outside repainted. I pulled the rad hoses & the heater hoses & only a slight bit of rust at the upper rad hose at the radiator. When I drained the radiator and block at the 2 petcocks, I only had green come out with no particles of rust floating. Any suggestions? Flush out the system; if so, how?

Thanks