Fleas are one of nature's tiniest villains. They bury themselves into people and their pets -- biting and making us itchy. Sandboxes are a common place for these nemeses to make their home, after they fall off your pet. Individual fleas are easy to get rid of -- but when you want to destroy an army -- you have to bring out your big guns. In this case, it's vinegar.
Remove all of the sand from the sandbox. Shovel or pour it into a strong garbage bag. Take it to the dump. Put it in the back of a truck, if you can, to avoid getting fleas in your vehicle. You may be able to put it at the curb for regular garbage pick-up, if there is a reasonable amount.
Wash your sandbox with a water and vinegar mixture. Mix about half and half in a bucket. Dip a cloth in it, and wash the box vigorously.
Let your sandbox dry in a sunny location. The sun's heat will kill remaining fleas and eggs that are attached to your sandbox.
Put fresh sand into the box. You can purchase the sand from a gardening store, or from a home improvement center.
Use a tarp to cover your sandbox when you aren't using it. This will prevent fleas and other varmint from entering the box.
Treat your pets and home for fleas, to stop them from re-entering the sandbox.
You can buy a cover for your sandbox instead of using a tarp.