Sorry but this post is why I don't answer any posts anymore on this site because then i get email everytime someone posts, get tired of deleting emails. some times we kinda over due it partially because people don't read all the posts jump in in the middle and ask questions already answered other times we have not thought thru what op said and other times op does not give enough information other times we have not thought thru what we are saying. I like answer above 5 minutes on phone talking at 200-400 words per minute versus typing for me at about 15 words per minute this could have been solved or at least a better understanding of what op wants. But we really beat it up sometimes, I personally if it is not my area of expertise, going sit on side lines and observe where as some folks want to be the hero and are way off track, that said in less i know exactly what is up meaning probably done it before(47 years of this stuff), this topic is not my area of expertise, but if was to hazard a guess radar probe with some tweaking, used in a lot of tanks of different purposes flawlessly. (I did what I am railing against)
I still enjoy reading posts but sometimes it is like this one just get it done. There is probably more than one way to solve this but we all know based on circumstances sometimes we don't get do or get to best solution for what ever reason, application unique or specific.
Sounds like you need level control in a tank +/- CM under vacuum with water and vapor or steam, referenced internally certainly will have the issues describe with reference tube Blown down might be a idea like in boiler world a lot of sensor have to be blown down at periodic intervals. also might add this have used some different pressure transducers in similar boiler condensate return tank (pressure tank not vacuum)with external blow downs to remove water vapor or sedimete from sensor system, when this is done usually takes sensor offline from sometime until temperature in dp sensor stabilize, did not like this again not my area of expertise but radar sensor?
So good luck getting what you need/want