A proper flush with water should do the trick. I do it a few times in a row. Warm the bike, empty it, fill with water and warm it up, empty it, fill it a third time, empty it. Fill with antifreeze and warm it up and top off the level.
I use distilled water to flush. Vinegar and water is a good cleaner but I don't use it unless I see signs of crud. If you use vinegar be sure to flush with clean water afterwards. The whole process doesn't take long. I leave the rad cap off so the bikes heats faster and builds no pressure. I drain from the water pump and pop the hoses of the drain valve.