I've just installed a new drain assembly from home depot on a new cultured marble bathroom sink. I followed the steps in this fabulous video to prevent leaks, including putty plumbers putty around/on top of the rubber gasket of the drain assembly that butts up against the sink (as shown in photo). Now, it's leaking at that connection.
I also installed a shelf in the vanity a few days after installing the drain, and may have jostled the drain pipe a bit in the process. I'm wondering if that perhaps caused the seal to break, but I also would think that the seal shouldn't be THAT precarious as I wouldn't have applied that much force to it, and it makes me worried what might happen when tenants do god knows what in there.
Should I re-install the drain & plumbers putty and be careful not to touch it again? Or is there anything else I can do to make a better seal in that location?
EDIT: i saw an answer get posted (and deleted?) suggesting that the seal should be INSIDE which was my understand at first too, then I wondered how that worked with the overflow drain built into the basin that leads overflow down to the drain pipe from INSIDE (i.e. below the drain entrance on the OUTSIDE where water normally goes down), which I assumed was the reason for the holes in the threaded part of the drain assembly just a little way down from the drain trim (as in the photo). I figured this is why the black gasket under the basin is a crucial seal and a potential point of failure.