Flush the system?

I was curious....is it important to "flush" the rad, pump, etc before installing new WC components? And if so, can you use just regular distilled water?

I only ask because I heard someoen talking about running the pump and rad before installing. I didnt do it with my first set-up, so I was wondering..should I have?

It can't hurt anything. If there's any junk in there, it's a good idea to try and get it out before you put it all together and it swims around your loop until it gums up something.

there are sometimes little bits of metal in the rad... just flush it with a tap.
pumps are usually clean

Personally I like to assemble a working loop outside the case and run it for a couple of hours to clean out all the possible junk in the system. This is after a good overnight soak of the rad w/a light solution of vinegar and water. I use a plastic tub for my "res" and it catches the small particles as they come through. The first time I did this (after tap rinsing the rad) I was surprised at how many little black specs there were in the tub ...

Ok, since I have 2 dogd and 2 cats, I was worried my new parts HAD to have SOME debris in them. I will run it with some water...and use a jug as a res .

You should always flush first. It can be suprising just how much junk is in the parts new. I still prefer to hook my setup to a kitchen faucet using a waterbed fill kit and force flush it out. I then rinse and drain with distilled. Using faucet pressure really flushes out any debris very well.

You also should do a few overnight water/vinegar flushings overnight before installing a new rad as new rads can especially have a lot of junk left over from manufacturing.