There is a run of DWV pipes (pvc) down to the main sewer tie-in in our basement. In two places along the run, the T intersection connectors have incoming pipe (in other words, where the drain from the toilet or the sink connects to the run) is turned into the down pipe flow. I'm not sure that makes sense so I'll try another way for clarity. There are a number of T connectors along the run which have a curved component. The plumbing subcontractor says the curved part should be toward the downpipe flow, but the contractor says it doesn't really matter.
Who is right? Or are they both right?
Any thoughts would be greatly appreciated.