In FengShui, one is said to have solid back-up in life when one house is having hill or mountain directly behind one’s house. Of course the hill cannot be too close and too steep.
However, if there is a sewage tank right behind your house, you are looking for troubles. You career will become stagnant and you will be facing financial problems.
A sewage tank symbolizes waste and dirt and to have it at your back of your house as back-up only means that you are doomed from the start.
The best solution is to move house.
If you cannot, please plant a row of trees to absorb some of the bad luck or bad Qi. Of course this will not eliminate the problems. The other way is to fill up a small pot with uncooked rice and place it at your back of your house to promote and capture new growth of luck.
But if can, the best is still to move house.