Hi @lsfarm -
Wow, this sounds like something nice indeed.
I do not mean to steer you away from your current direction of thinking, so I am only offering my opinion and ideas
I usually opt for the most simplistic solutions. In your case I would probably work with a small load cell as apposed to a pressure sensor. Mostly because I have work with them a lot (between 0.1kg and 200kg) and they rend to be quite reliable and easy to get working The challenge you might facing with either pressure sensor and Load cell is the weight of the ice. I am nor sure what accuracy you are hoping to achieve, but it is something you might need to consider in your vat design.
Another way (probably more accurate) would be to have a electrodes inside the vat at i.e 25%, 50%, 75% and 100% . If course these will need to be shielded from the ice in order to only detect the tea. This can be easily achieve by utilising some sort of perforated housing inside the vat, small holes to let tea through but too small for ice to affect the electrodes.
If you do not require extreme accuracy, I would consider load cells.
Sorry, I have not used these before.
Hope this helps in some way