Take the arrangement out of its container. If the stems are stuck in floral foam just pop the whole thing, with the flowers still in the foam, out of the container. If the flowers only support system is the container, wrap a rubber band around the stems so that the arrangement doesn't lose its shape.
Set the flowers inside the bathroom shower. Set the water to cold and let the spray wash the silk flowers clean. If you don't have a shower, put the flowers into a sink that has a spray nozzle and spray them with the nozzle.
Turn the water off and gently shake the flowers to remove some of the water.
Let the flowers air dry before putting them back into the container. You can do this by laying them on the floor on an old towel.
Take the silk flowers out of the container. Make sure to leave them stuck in the floral foam or to wrap a rubber band around the stems so that the arrangement doesn't lose its shape.
Pour a cup of kitchen salt into the bag. Salt will gently scour away dirt and dust from the flowers and leaves.
Put the flowers into the bag with the stems facing the opening.
Twist the top of the bag closed and hold it shut with your hand. Shake the bag for about 30 seconds.
Remove the flower and put it back into its container.