New Vessel sink is leaking at the spud gasket.

Remove it, (Don't forget water will come out when you uncscrew it!!!) clean it thoroughly, especially the ends, clean and check seating of any rubber washers to make sure they are fitted correctly and not being distorted when the rings are tightened, reseat it with no force (it should sit naturally without having to force it in) and tighten rings. There are lots of videos on youtube showing how. If you cant stop it leaking buy a new trap. It's worth while looking very carefully for exactly where the leak is before you remove the trap, it might be coming from higher up. Repair Leaky Sink Drain Pipe

silicone will seal any water and make to not move .

Use silicone to seal the flange and teflon tape on the threads that the drain flange screws onto. make sure that the sink isn't cracked. make sure that you have a washer under the rubber gasket that seals the bottom of the sink and tighten the nut against the washer snuggly.

are you talking about the drain assembley?

THE PART YOU ARE TALKING ABOUT IS CALLED DRAIN TAIL PIECE. THE DRAIN YOU CAN REMOVE BY LOSENING THE NUT UNDER THE SINK WHILE SOME ONE HOLDS THE DRAIN INSIDE THE SINK FROM TURNING THE OART KEAKING IS CALLED A SPUD GASKET WHICH SEALS THE DRAIN TO THE SINK

a waste with a over flow does not work well with a vessel sink because the sink is to thin

have the plumber pop an opening on the side of the drain pipe under the sink. and add a indoor vent.

https://www.ekbdc.com/index.asp?PageAction=VIEWPROD&ProdID=11188

YOU NEED A DEROSE DRAIN ITEM# DD-353,PUT A LINK OF THE PLACE WHERE A SEEN THEM, GOOD LUCK

Put plumbers putty around the flange that will be in contact with the sink. When you put it into the hole, try to line up the overflow as good as possible. The nut that goes onto the bottom (tailpiece) has a rubber gasket that will go between the nut & the sink. Adding some plumbers putty here won't hurt. After all is secure, just remove the putty that squeezed out from tightening.