The best solution is to replace the pump first.

Then disconnect the return line from the steering box to the pump.

Get a helper and start the engine.

Fluid will pour out of the open return line, so have a bucket ready.

Add new fluid to the reservoir as fast as you can. While doing this, have the helper turn the steering wheel all the way to the stop on the left and then turn it all the way to the stop on the right.

This will flush all fluid in the box.

Stop the engine and check the fluid in the bucket. If you find any metal particles, repeat the above process for a second time.

Have quite a bit of fluid ready. I think I used three quarts in less than one minute.