Pressure sensor unstable after Arduino power off/on
The sensor has two holes. On first big, you have the attachemnt of the hose. Second is below your sensor, it is breathing hole that transmits atmospheric pressure. Since you have poured the sensor with silicone and submerged into the water is clearly no go solution. Remove the silicone and attach a hose, and use the sensor like in instruction manual. 
I suspect you want to measure level of water continously, in that case the hose will leak pressure at long term, and it will be useless. This kind of sensor are used in maching machines, where the water goes away and then is filled again, air leaking trough the hose can be neglected.
Since you already flooded the sensor, install a hose and bore the wall at the bottom, put the sensor in upside down position, externaly - not submerged obviously.