It's always a judgement call, and very site specific. It sounds like you may have a blend of some or all of the following, codified for PA, USA, but #'s are very typical of other places. Start here:
Per Pennsylvania Code
changes effective through 35 Pa.B. 1322 (February 12, 2005).
TITLE 25
ENVIRONMENTAL PROTECTION
CHAPTER 73. STANDARDS FOR ONLOT SEWAGE
TREATMENT FACILITIES
§ 73.17. Sewage flows.
Source:
Type of Establishment
Commercial Gallons/Unit/day BOD/day
Stores (per public toilet) 400 2
Bus service areas not including food (per patron and employe) 5 0.02
Restaurants (toilet and kitchen wastes per patron) 10 0.06
Restaurants (kitchen and toilet wastes, single-service utensils/person) 8.5 0.03
Engineering is the practice of the art of science - Steve