Waste Tank - When Nothing Comes out!

[GA1817]

I was going to dump my waste tank but when I pulled the handle nothing came out The cable appears stiff but does push in and out and does not feel broken. I researched the threads and found people with similar problems but never the solution as to what the potential problem could be. I am going to drop the bottom plastic but was wondering if there is any way to manually operate the valve if something is wrong with the cable. We do full time so I need to do something soon I always leave the valve closed until dumping and use the back flush after every dump.