On my 08 Allure the grey and black tanks are sort of L shaped and sit on top of the water tank. The sensors are stuck to the wall of each tank inside the L. You have to put your hand up and find them by brail. The black Tecma sensor is in the same area, I have just replaced the Tecma mid sensor which has fixed the false reading problem on its display. Perhaps the use of a mirror and torch will assist in locating them.
Now if you are getting erroneous readings on the seelevel sensors check the proximity of any metal, loose wires hanging, or wire supported hose. I had replaced the hose connection to my water pump with wire supported hose and it was too close to the sensor panel and caused faulty readings. In replacing my Tecma sensor the same happened with the wiring from that and had to tie that clear.
In the UK with;
2008 Allure Sunset Bay