I just tried to install two identical Price Pfister faucets into new Kohler undermount bathroom sinks. I followed all directions installing drain using plumbers putty, etc. Tightened the plastic nuts underneath onto rubber gasket. Both have leaks I can't stop. Have done this numerous times w/no problems. Any ideas?

Hi Jim...

Back that nut and washer off again... install new putty up top and then add some PIPE DOPE to the threads underneath... ;) ALthough this is not usually required, some of the ALL PLASTIC pop-up assemblies seem to need this to button all up nice and tight!

Slide the neoprene washer up and tighten the nut. Do NOT overtighten here. Hopefully, that fixes this for you.

You did add pipe dope or teflon tape to the threads of the 1.25" tailpiece... right?

Let us know how you made out.

MARK