Cooling system flush?

My waterpump is leaking and I will be changing it along with thermostat, housing and possibly the fan clutch. I'm going to flush the system as well. Should I flush the system before I put the new pump on or after?

Before! You want to flush with the old equipment. Then put in the new stuff... Unless the old stuff simply doesn't work.

If you are planning to run a chemical flush do it before you put on the new pump. Then, drain the system, remove hoses, thermostat cover and water pump then you can flush the block, radiator and heater core with a garden hose before putting it all back together.

What are you driving? Other than a leaky pump why are you replacing other parts, just maintenance or are you having other issues??

Just maintenance. I've decided against replacing the fan clutch and the thermostat housing. Just the waterpump, outlet pipe, and thermostat. 2001, 4.0, AW4, NP231 with 223000 miles. The fan clutch was new in 2009 and has about 80000 miles on it. Seems fine. Finished flushing it and I'm just waiting for it to cool so I can drain it and get started.