3 inch to 2 inch

Question for the group. I presently have a double vanity that is drained by a two inch pipe. It is vented by a 3 inch DWV. The 3 inch waste passes through the floor and I would like to reduce it to a two inch pipe to connect to the main waste line. Would this be against code or do i need ti leave it as a 3 inch pipe. Also the distance to the waste line is around 6 feet

Do not confuse a vent with a drain...if it only serves as a drain for the vanity, it could probably be reduced to 2". But, it probably also has a connection to the toilet and tub, so, no, it must remain that size. And, if it is actually a vent for things below, it wouldn't pass code today, as you're using it as a drain and wet venting between floors is no longer allowed and needs to be at least that size to work well. Last kicker is that even in your own home in MA, it's illegal to do any plumbing...a pro would know what is required and how to do it properly. Many states allow a homeowner to do plumbing in their own home, but they all require a permit and an inspection. Failure to do so could get expensive and potentially dangerous.

Jim. Thank you for the quick reply. And I understand.

I'm pretty sure that Massachusetts does not allow DIY plumbing at all. I'm not the plumbing police, but it would be wise to check this out...I've been wrong before, but if I'm correct you could be in deep doo doo if/when this is discovered.

Your description implies that you want to take a 3" drain line, reduce it to 2", and then connect it to a 3" line. if that is actually what you mean then the answer is NO, you cannot "reduce" a drain line in the direction of flow. The distance to the drain line is completely irrelevant, and while the vent MIGHT be able to be reduced in many cases, and it depends on the code and situation, it may be required to remain 3" all the way to the roof.