What is the best way to go about cleaning a NUK 5?
If it's just dusty from kind of being kicked around, I'd wash it like you'd hand wash any kitchen utensil. A little dish soap and lots of water. If you are particularly concerned about germs, a very VERY weak solution of clorox (we're talking a tablespoon per GALLON of water). A couple of minutes soak, shake off the excess solution (be careful not to get the bleach solution on any blothes) and let it AIR DRY.
Don't know about NUK's but many pacifiers are top-rack dishwasher safe which would be a good way as well.
If you are concerned about germs, I have seen many sites for chronological babies recommend putting the pacifiers in boiling water for about 5 minutes. This should kill all germs on them.
They also recommend using distilled water, as the usual water from the sink contains quite a lot of lime. This will then stick to your pacifiers and if you boil them repeatedly, a milky layer will build up on them. AFAIK this is not a problem for your health, but you might dislike the changed feeling.
There are also special sterilizer devices just for this purpose. I suppose you should be able to buy them in a baby store near you.
To sanitize water needs to be 160 F or hotter. Most taps will not go above 140 (and frankly, most are set to 120 to avoid scalding issues).
I just microwave a cup of filtered water with a chopstick or wooden skewer in it and then hold the pacifier down inside of it for maybe 2 mins at most. Also if you press down on the teat/nipple the inside might fill up with water a bit so I always have to get out the water as best I can.
I use dish soap and warm water usually but sometimes I will boil mine to completely sanitize them.