Two fairly universal reasons why grease recovery can be a problem rather than a solution are improper sizing and improper maintenance. The first problem is easily solved by referring to Standard PDI-G101, published by the Plumbing & Drainage Institute. An easy but comprehensive method is included in Appendix A of this Standard, which can be viewed and downloaded from the PDI Web site at www.pdionline.org. The basic method for sizing grease interceptors is shown in Table A1.3 of the standard.
For dishwashers, a separate grease interceptor is recommended for each commercial unit. The size of the interceptor is determined by the gpm discharge rate of the dishwasher as specified by the manufacturer. Select an interceptor whose flow rate is at least equal to the gpm discharge rate.