Assume My Dump Valve is Closed and Won't Open !

The most cost effective solution will be a septic pumping service, you will be able to save a bunch of money because you can take the rig to them, saving a trip charge. To pump out sewage you are going to need a trash pump, they are big, heavy and tend to leak. Most are gasoline engine driven. You can rent them very easily at most any rental company, but that will be on nasty job. Since the valves are working but apparently are becoming sticky, change them now. They cost about twenty five bucks, and are very easy to install. Not worth waiting until the current ones cause a big problem.