A product page for a bathroom sink states a "rough in valve" must be purchased separately for the purpose of installation. I wasn't sure if I really needed that because I am just going to replace my current faucet and there should be an existing valve under the sink, but the check out page reiterates that the valve is required. I did a bit Googling and on another forum some folks also mentioned the necessity of the valve. The product page claims the valve, by the same company, is specially designed.

I am stumped because it seems another faucet model from the same manufacturer does not require a valve. And the views on that other product page make no mention of a valve requirement and talk only about how easy the installation is. So do I need to purchase a valve for a faucet replacement job? Do some faucets require special valves? In what ways if any are the two faucets different in installation?

Also what's the difference between valve assembly and drain assembly? Do they ever overlap? I know what a valve is, but I am not sure what valve assembly and drain assembly are respectively. Google and Google Images have left me more confused as they seem to give various pictures of different things.

2 Answers 2


The first product is a 3 finish piece faucet and in this case Moen has turn it into a feature where you can just swap out the 3 finishing pieces without touching the underlying valve. You need to buy the valve separately and it is specific to that series of three piece faucet.

The second link you have is a single piece faucet that has everything in it.

  • +1 but I am still not quite clear how three piece faucets and single-piece ones differ in terms of installation and their connection to the valve. By "the underlying valve" do you mean the special valve that is required?
    – Eddie Kal
    Oct 3, 2019 at 3:05
  • If my current faucet is a three-piece, do I still need the Moen valve?
    – Eddie Kal
    Oct 3, 2019 at 3:08
  • One piece has a threaded connection that fits down into the hole in the countertop and you hookup the hot and cold to it. This moen three piece has a single valve body that sits under the counter and you screw the handles and spout onto it from the top, allowing you to swap to different handles/spout later. The moen valve is proprietary. Other three piece faucets maybe different. The link is only to buy the handles/spout so you'd need the proprietary valve as it doesn't come with it. Showers work this way with a rough in valve and then you pick the trim kit. Oct 3, 2019 at 3:11
  • If your current 3 piece is from the same moen line then the valve body should work. You'd have to check part numbers. Oct 3, 2019 at 3:12

The "rough-in valve" is the mechanism and plumbing for the pop-up drain plug and also the bare valves that go below the handles


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