Neat project. I spent a few years selling level instrumentation into the water/wastewater industry and it can be a complicated problem. In my experience the sensor technology, build quality, and firmware matters a lot; with ultrasonics the echo processing algorithm is extremely important and dealing with false readings can be a pain. I'm not familiar with the sensor you linked but am interested to see how it performs; my guess is you won't have any real issues if the tank is fairly small. Be aware that some wastewater applications (particularly digester level measurement and the like) are classified areas and require explosionproof or intrinsically safe electronics!

Thanks for your interest. I posted this project to put this idea somewhere since I cannot "jump start" it right now. I will publish my experience as I go.