I am a licensed plumber in California where we go by the 1997 UPC. When I install a typical residential drainage system in a crawl space before subfloor is laid, I usually vent the toilets as follows: the 3" line desends vertically from the toilet to a 3" combo @the building drain or branch thereof. Just downstream or upstream of the combo I install a 3x2 sanitee for venting with the branch vertical or rolled no more than 45 degrees. I have used this method for many years and been inspected by many inspectors, but now an inspector has called out for all the sanitees (3 for toilets and 2 for showers) that are used in this manner be replaced with combos or other drainage fittings. I have talked with 3 other inspectors in other towns and they all agree with me and say it's common practice. The UPC doesn't say I can't use this method, but doesn't directly say I can. The UPC Illustrated Training Manual does not have a picture exactly like this method but I did find one in the 1982 manual. I am 99% sure I'm right and am looking for more proof or advice on how to proceed.