Trying to detect when a drain pipe, filled with water from a washing machine pump, starts to get backed up.
Since the water is being pumped through, a simple water detector is not enough. And since the water is being pumped and draining, but slowly (Too much water volume for the pipe in a small amount of time), I don't know if a float sensor will work (downward movement from pump, upward movement from backing up).
Also, the pipe is about 2.5" in diameter. The sensor should interface to a 3.3v or 5v level, or simply open drain, but I can figure it out from there if I need to level shift. It should be water tight to prevent shorts or anything (Though I don't know the proper safety method for this).
Is there any standard way of doing this? The microcontroller (a msp430) will not be submerged or anything, just the sensor.
Edit: Picture/Diagram as requested.
Setup is essentially exactly the same. Pumped water goes down "standpipe", as does the backflow up. My main access is only at the section marked "Indirect Connection, a 2~3" diameter pipe. The Waste Stack is probably 4~5" diameter. There is a sink that is in parallel with the washer machine, and water sometimes backflows out of there instead of the "indirect connection", as it is a few inches lower.
Ideally, the sensor could fit and work right above the trap in the diagram, without clogging the pipe itself. I might be able to add a t-pipe between the trap and waste pipe, but I want to avoid that if I can.