Ashely,
You have 2001 right? If so, I believe you will have Dupree Products dump valves and actuators. Dupree has recently vastly improved their web site. You can order most anything you need online now. There are also parts breakdowns of the twis-loc valves that are used on our coaches.
http://www.dupreeproducts.com/
There are two phillips head screws pointing down located on the top of each valve near the actuator rod. Removing them allows one to pull the guts of the valve right out the top. Be sure you have followed Tuga's advice and the tank is empty before doing this. Once out you can easily replace the gasket portion and you should be as good as new again.
Be sure to clean it up well and the label suggests lubrication with axle grease. I use a silicon free dialectric grease and it works smoothly when completed. Good luck. Russ