Black Tank Help Needed

Update: It looks like the problem is solved. I talked to my brother who also lives in a camper. He said, If you have a black tank flush why don't you use it? I was concerned it might overflow, but the meter was reading only 1/3 after I dumped today. So I connected the back flush and opened the black tank. I watched the water through the clear opening and it started dirty but kept flowing so I left the water running until it became clear. Then I checked the meter inside and the black tank says E which means it's empty. So now I'm a happy camper again. Thanks for all the help. I'll keep doing the back flush after every tank dump.