the MPX4250GP sensor seems to have that restriction.I would like to find one that did allow water.
I think these sensors are used a lot in washing machines as you describe. That seems to work well since the air tube is re-primed with air ever 20 minutes. But I think that if it is not re-primed for 20 days, the air will go out, causing wrong readings. Like a balloon. It will hold air for 20 minutes fine, but probably not for 20 days.
Any easy way to re-prime the air hose before a reading? Readings normally ever hour.