Any thoughts on estimated wastewater flows from fastfood restaurants compared with typical sitdown restaurants? I'd expect more from the sit down but.... Any flow ranges you'd speculate on? I've seen the Handbook numbers but they don't break it down.
Go to your local water supplier and ask them if they'll give you water meter readings from several fast food restaurants in your locale. You should be able to get an idea of average daily flow this way. If they have peak hour flows that would help a lot but handbook peaking factors are available, if not.
Restaurant with drive-in (typical fast-food) : 60 L/day per parking or seats. Otherwise, 50-75 L/d per employee. These are the design criteria accepted by our local authorities.