Choosing a watch with a nylon strap is a good idea if you plan to wear the watch on a daily basis. Nylon is an extremely durable fiber that can last for years if maintained properly. Unfortunately, the weave of the fiber in the band can trap small particles of dirt that can cause staining and odor. Cleaning the bands, however, is a straight-forward process.
Remove the nylon bands from the watch. Using a small screwdriver, push down on the spring bar until it comes away from the lug of the watch chase. Repeat with the other side. Remember to save the small bars.
Fill a small bowl with water. Add a small amount of laundry detergent and mix it.
Put the dirty nylon straps into the water and let them soak for a few hours.
Remove the straps from the water and squeeze gently to remove excess water.
Allow straps to dry overnight. Repeat the above steps if the bands still appear dirty.
Re-attach the straps by inserting the spring bar into the case-end into the dry watch bands. Insert one end of the spring bar into the case lug. Manipulate the pin to line up with the other end of the pinhole on the other side of the watch case. Use a small screwdriver to do so, if needed. Repeat with the other side of the band.