The laundry room (DWV) in the house I recently purchased was plumbed as shown in the following photos. It has an inverted sanitary tee connecting two vents. Is this correct or should it have been plumbed with a tee?
That is the correct way to do it. Many areas don't allow tee's in a DWV system. Before you reinstall the dry wall be sure to put nail plates on the studs that the CPVC goes through.