The more I think of this , I'm really surprised that the end use allows the use of a DP cell , which would be very difficult to clean to a food grade standard . Most of the food customers I deal with wouldn't allow anything like this .
It would have to go non-contact , eith ultrasonic , and it could be fitted to the existing setup , or possibly to load cells , and weigh the tank .
Ultrasonic is probably the best way to go , with simple on off control and a bit of a dead band to prevent cycling .
I don't think you will get what you have to work very well , there is miles too much disturbance in the tank to get a good valid pressure signal , and it also seems that it is not particularly hygenic , though of course this is your customers cal .
Where did you say it was ......