Which of the following is a condition for installing a combination plumbing fixture on one trap

This statement is incorrect because the installation of a grease interceptor is not directly related to the spacing of waste outlets in a combination plumbing fixture. While grease interceptors may be necessary in certain applications to prevent grease buildup, they do not influence the conditions for the distance between outlets.

This choice is also incorrect as it pertains to the sizing of the trap rather than the conditions for outlet spacing. While it's essential for traps to be appropriately sized to handle combined waste, the specific diameter requirement does not relate to the maximum allowable distance between the outlets.

This option is misleading, as the depth difference between compartments does not directly affect the spacing of waste outlets. Although equalizing the depth may be a consideration for drainage efficiency, it is not a stipulated condition for installing a combination fixture on one trap.