If you are having issues, might want to consider using a float sensor - simple and super reliable even in pretty hostile environments. Mine has been working now for over two years without a hiccup. Basically it’s a stainless steel rod with a float outside that changes the resistance as it moves up and down the rod. As much as I wanted to use something like a sonar or pressure sensor, I went for a float sensor as I suspected that otherwise I would be continually replacing sensors… 
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