A small suggestion.
It would be very convenient if the high and low water marker were around the entire circumference of the unit. This would allow you to see them no matter which way the unit is oriented.
+1, and in a high contrast color actually readable.
I drew on mine with a black Sharpie. Seems to help.
@john.jcb That would help - I agree! Will share this with the team - if you have any other thoughts or suggestions, let me know :)