If I may add my 2 Belgian franc's worth, is the level important, or is the mass of the liquid the main thing?
I've worked on fuel depot equipment (the place where those gas tanker trucks fill up), & the products were sold by weight, not volume. We measured the average temperature of a delivery (35,000 litres sometimes) & corrected to the weight (mass) at 15°C.
If you use 2 pressure sensors (max & min) at the bottom of the tank, you should be able to run the whole show with a couple of relays.
(This isn't for a toilet flush system, is it? There are simpler ways! ;-)

Jay, maybe we should ask more questions before replying to this kind of thing!
But, like life (most times), it's all good fun.

Regards,

Richard

P.S. On pressure sensors, a remote way of doing it is to use one of those aquarium aerator pumps with a tube down to the bottom of the tank, & put the pressure switches in the air line well out of the way of the liquid!