Our Flatpack sensors can be adjusted to ignore non-metallic tanks and containers (plastic, glass, fiberglass, etc.) and detect the liquid on the other side.  It attaches to brackets, filling machines, or whatever you can envision.  Customers have even used two sided tape to "stick" them on filling containers for inexpensive, trouble free operations.   Customers have used them in applications ranging from very small plastic bottles to huge tanks.  [see example]