Leak from base of American Standard faucet

[Jimmy P]

Its an American Standard bathroom faucet, maybe 4 months old. The water is dripping from the underside where the two plastic "nuts" screw into the faucet. First I tryed hand tight on the plastic nuts, and it still leaked. Then I carefully used some vice grips and got them even tighter, but they still leak. The surface of the sink looks prety straight from what I can see, so I can't figure out they its leaking.
I dind't apply any silicone or plumbers putty on the faucet when I installed it because it came with a gasket, as you can see in the picture below. Should I add some silicone or plumbers putty? I know that the water must be coming in from were the bottom of the faucet mates to the sink, just not sure how to go about making a tight seal. Thanks for any responses.

 

[Jimbo]

If the only leak is water coming under the base of the faucet, then take it out,and put putty or silicone under the base. That plastic piece is probably referred to as having "caulk grooves" in it. It is meant for that.

And for pete sake, replace the supply lines and NEVER use teflon tape or pipe dope on gasketed fittings like that.

 

[Sponsor]

 

[Runs with Bison]

When I put them in I roll a long thin rope strand of putty and lay it along the gasket grooves with a small overlap that I squeeze together. The rope compresses to fill the space with no gaps when I tighten the plastic nuts.

This way produced less excess that squeezed out during compression or was visible later than when I just dabbed putty in there and tried to shape it with my fingers. I stumbled onto it after my 3rd or 4th one and it has made my subsequent installs cleaner/faster. There was a particular American Standard faucet that I put in every house I lived in for years; it had a long neck with a high termination that allowed more clearance for stock pots.

 

[Jimmy P]

The reason why I didn't initially use silicone/plumbers putty on the base is that the instructions didn't state it, so I figured that gasket was there so you dont have to use any.
As far as the pipe dope on the supply lines, I put that there because initially I thought thats were the leaks were coming from. At first it was a very small leak, that would drip from the black plastic nut, onto the threads, and end up on top the supply line fittings. You can see why an amature like me would think the leak was from the supply line at first. It just a little hard to see at first under the cabinet. Thanks for the respsonses guys, I will try it out that pipe dope.