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Deleted member 26818
Crude = less to go wrong@spinlondon It will be too crude.I found these View attachment 49480
that can work that way but still to much mechanical movement involved.
Like @Rob said above a good solution is a pressure sensor transducer.It seems the most logical. I found this, View attachment 49481 which is not cost prohibitive.
I found a second solution like you say but it works with the resistance of the water.View attachment 49482 and is just 40pounds.
The first ones you show, require drilling into the tank.
If you want to go crude and drill into the tank, attach a clear plastic tube on the side of the tank, with an orange ping pong ball inside the tube.