What is the cabinet industry's standard practice for cabinet depth for built-in kitchen appliances, specifically a trash compactor? Is the cabinet depth based on 1) the case of the appliance, or 2) the minimum depth of the opening/cutout specified by the appliance manufacturer? In my situation, the case of the trash compactor is 23 inches deep [24 inches including the drawer front] and the minimum depth of the opening/cutout specified by the manufacturer is 24-3/4 inches. What depth should the cabinet be for the trash compactor? Thanks.

Always follow manufacturers' printed instructions. If they say the minimum depth is 24 3/4 inches, that is the minimum depth you should provide. However, I'm surprised, because base cabinets are ordinarily 24 inches outside to outside, and if they are made from 3/4 inch stock, the depth available would be 23 1/4 inces at most.