I saved this set of instructions that was posted by dougrainer about how to solve the problem. Maybe it will help you.
dougrainer wrote:
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IF you have the standard 3 inch valve with the pull handle. The pull handle has BROKEN loose from the knife valve. NOTHING you do externally will open it. What you have to do is, connect your dump hose and install in sewer drain. On the opposite side of that pull rod on the valve body, you drill a 1/4 inch hole thru the plastic valve body and then insert a 1/4 inch rod (most phillip screwdrivers are 1/4 inch or sl;ifghtly smaller) and shove the internal plastic knife valve open. LEAVE that screwdriver IN or you will get a little sewage out that hole and have the 1/4 rod avaiable immediately after drill that hole to prevent excess waste from coming out that hole. Then replace the complete valve after flushing out the system.
Let us know how you solve the problem. Good luck.
Fred