Your holding tanks are ALREADY portable as long as your trailer has wheels. It would make MUCH more sense to hitch up and take the trailer to the nearest public dump station in one trip (as opposed to making several) where you can dump tanks AND fill fresh water tanks at the same time. If there is no public dump stations near where you are staying, MOST RV Parks will allow you to use their dump stations for a very reasonable fee. State parks are another possibility for using the dump station. Usually you just pay the day use fee.
Good luck / Skip