Your probably right on about the pressure testing, but still I'd rather error on the side of caution when ever it could mean blowing some money.(no jab intended, just a paranoid person here,lol)

Oh, i found something that will get most stains out of tubing prestone radiator flush, I ran some through some tubing as a test and it removed blue die rather effectively. This was on a vinyl type tubing so someone might want to test it on other types of tubing, I woulndn't recommend it for acrylic parts though.