i'm not planning on just dunking them into the solution, what i'll probably do is have a tall curved piece of plastic made of a quartered pipe and a straight piece of plastic with holes drilled in and the pressure sensor nozzles pushed through. Then I'll have them glued together and the bottom glued up and weighed down before putting some kind of hook on the top so I can hang it off the side of a barrel. If I do it that way then I can probably calibrate it for each barrel and move it around. The only complication remaining is working out which sensors to use. I can only assume that beer isn't corrosive since you can leave it in a plastic bottle for years and nothing will happen so I'm planning on getting any that are suitable for water but I need ones that will be accurate enough and I don't want to pay loads. There's hundreds on RS Online so I'l just have to spend some time going through them.