Leak on sink tail

I have a brand new Kohler sink and a Moen valve and trim kit (Model # T6205 + 9000).

I installed the tail and all of the plumbing with little problem, except a little annoying leak.

The problem seems to be where the collection of large rubber tapered gasket, large washer and large nut interact. There doesn't appear to be a leak between the rubber and the bottom of the sink drain opening, but water passing between the rubber and the threads of the tail piece, and washer and large nut. I thought I might actually have too much pressure, but loosening it just makes the problem worse. I'm wary of applying too much pressure and breaking the sink.

Is there a "trick" that I'm missing?

Thanks!
Ben

I 'll assume this is a lav. Is this the average Moen plastic popup assembly? If so, it'll break before the sink does. Once, I found that the openning in the bottom of the sink was irregular, told the client, and used silicone sealer. I'm sure there are other approaches to be found here.

pack the threads on the drain piece with plumbers putty. Rub the putty into the treads with your thumb, but rub it so all excess is removed and you just have putty in the threads.

It's all metal construction (chrome plated and stainless steel). I've got lots of plumber's putty so I'll try that. Any reason not to do both the putty and a bead of caulk right where the rubber and pipe meet sandwiched in between the washer and the rubber?

I apply Teflon paste to the threads where the mack washer lands...
No Leaks Here!

drain

If you EVER hope to remove that drain someday, DO NOT put putty on the threads. Use a pipe dope in the area between the rubber gasket and the large washer, then tighten it as much as possible. If the sink breaks it was defective, because it is almost impossible to do it otherwise.

apply pipe dope on both sides of the the rubber and a little on the threads. make sure you are putting the friction ring against the nut. Make sure you have plenty of plumbers putty on the strainer itself where the chrome or metal meets the porcelain. Don't put any plumbers putty on the threads it will actually hold you up from tightening it. When you tighten it use small jerking motions not one steady tighten. It definitely helps in this situation. good luck