holding tank flush questions

We have a 2006 Liberty Prevost. We are obviously new owners... you will see why i say that in a second.

We live in Dallas Texas and keep the bus on a new small farm an hour north of Dallas.

It has sat on our new farm new barn pad site for about two months with some amount of waste. When we closed the gray water bypass, sewage from toilet backed up into shower. When we opened gray water bypass the shower drained. When we finally got septic tank I tried emptying the tank. It shows 80%. For the longest time it showed only 20%. Something went down the drain (know this because the still open drain line in the barn well stunk. Flushed that with clean water. Smell gone. Good. BUT tank shows still 80%. Put RidX and then half a large bottle of dawn. Left it sit for a week. Opened the drain value. Not much came out. Still showing 80%. Bought Tyvek hazmat suit, suited up and gave the tank an "enema". What went in seemed to come out but gauge still says 80%.

Is there someplace to really connect a flushing hose to really wash the entire tank? What do we do? HELP!

Identify the holding tank. Identify the microcompressers for the tank level sensors they will be in the plumbing bay and look like a small fish tank air pump. Should have a small green led lit. Determin what one is conected to the holding tank. Remove the hose at the compressor and blow air into it till u hear bubbles in the tank. Recheck. If still wrong go to the 90 degree push in swivel fitting directly on top of the tank where it goes in. Remove the hose there cut 1/4 in from the hose reinsert recheck.

If you have the Tank Sentry by Headhunter, what Joe suggests should work. You an also remove the plastic hose from the pump and the gauge should drop to zero.

I believe some Liberty coaches used an in tank sensor that's based on a sonar like system.

It may be worth a quick call to Liberty during their working hours. They call tell you what system they used and may help you correct the error.