Hi,
I am installing new DWV for a bathroom under UPC. I would like to drain a tub/shower line (1 1/2") to a branch drain line (3") with a 1 1/2":3" coupling. The tub/shower will be vented before it gets to the coupling. Is this allowed under code and/or is it a bad idea for any reason? I think I read somewhere that drain connections can only go one pipe size larger.
Thanks,
Tom

Hi Tom:

If you branch off with a 3"x1.5" WYE fitting with an end cleanout in it you would be following code more closely!

Here, need to end the run with a full size cleanout before reducing the drain line to 1.5". For example, the drain is clogged by a rag...you retrieve down the drain line with a snake, but when it gets to the reducing coupling you propose the rag and snake get bound up and you can't pull the snake back. If had a 3" cleanout you could go down that cleanout and easily retrieve the rag... sound about right?

Anyway, that is what I would recommend if you can do it... ;)

MARK