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I have seen this done both ways. I put my plumber's putty on the sink in a circle that meets the bottom of the sink or top of the ring.

I have seen others attach the putty to the underside of the flange.

What are the positives and negatives of each and which is right?

On the sink

enter image description here

On the Flange

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    Looks like it may depend on what hands are doing the work.
    – Michael Karas ♦
    Jul 29 '13 at 19:16
  • They could be the same hands!
    – DMoore
    Jul 30 '13 at 0:48
  • :-) Could be. If so then I guess they learned how hard plumbers putty was on skin after the first go at it.
    – Michael Karas ♦
    Jul 30 '13 at 4:18
  • I am thinking after the first install that the baby oil on the hands got slick so he changed to latex gloves. I love the half a tub of putty on the flange in the second picture.
    – DMoore
    Jul 30 '13 at 4:20
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There is no "right way", but the "theory" is:

On a loose fitting (fitting has play inside the hole), placing the putty on the sink will create a better seal on the area actually making contact. On a tighter fitting, placing the putty on the flange will seal the areas closer to the center leaving less room for voids. See this diagram (tight fitting on top, loose fitting on bottom, "risk" for voids/incomplete seal in red):

Updated(2): Diagram of Flange and Plumbers Putty

Honestly, while the "theory" isn't bad, in practice it simply requires that you use enough putty to make a good seal. The net effect is that the putty just needs to be sandwiched between the flange and the sink to prevent water from leaking, either from an (intentionally) stopped sink into the overflow (bathroom) and thus down the drain, or from around the flange into the cabinet below when the flange acts as a reducer or on sinks without overflows (kitchen).

So, whichever way works best for you is the "right way".

Edit: Updated diagram to reflect the proper amount of putty. Edit(2): Updated diagram to reflect proper amount of putty including over-puttying.

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    On the right side pictures - wouldn't that make a case to not do it that way? There would always be water there right? Just thinking that water trapped in there won't evaporate as easily as it would on top surface.
    – DMoore
    Jul 30 '13 at 22:26
  • There would always be water there if you didn't use enough putty. This question/answer may help: diy.stackexchange.com/questions/30109/…
    – John Smith
    Aug 1 '13 at 1:05
  • Very true @DMoore and it was just a rough sketch -- my main point I was attempting to make was that in either case, you want to use enough to make a good seal.
    – Jacob S
    Aug 1 '13 at 14:20
  • update to reflect how it looks with the proper amount of putty (at least). I just follow my personal code of, it's not sealed until putty squeezes out all the way around.
    – Jacob S
    Aug 1 '13 at 14:29
  • Great pictures! Really explains the geometry.
    – Alex Feinman
    Aug 1 '13 at 14:48

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