RE: adjusting flow in a commercial style toiltet; my shop's toilet does not flush properly and sometimes does not flush. I tried adjusting the PRV at the water supply, the nut on the flush unit, replacing internal parts as well to no solution. Is there an optimum supply water pressure range; how do I adjust the toilet flow so it flushes correctly; is my unit worn beyond repair and how can I test to see if it or something else needs repair or replacing?