Standpipes are sometimes used when a "reserve" fluid quantity is desired. The BT-13 fuel system is an example. It had two 60-gallon (US) tanks, but a 3-position fuel selector. The right tank had a standpipe at the 18-gallon level IIRC, such that if the unwary student consumed fuel down to that level, and the engine sputtered, there was still 45 minutes fuel available by selecting the "reserve" position (ie the bottom of the tank).
