Redarc tank level sensors: TLSEN175, TLSEN200 and TLSEN225 in stainless steel at 175, 200 and 225mm, plus the TVMSDBWK-002 5 metre cable kit to connect them to TVMS Prime systems.
These are immersion sensors with no moving parts: no float to jam or scale up, so they last even in grey water and in tanks that sit unused for long periods. Length is chosen on the internal height of the tank, not on its capacity in litres.
The reading goes to the RedVision display or the TVMS module, shown as a percentage with voltage and consumption.