A sink question

My faucet died, so I grabbed a new one to replace it.  The new one came with a new sink drain tube.

When I install it, the rubber gasket on the top side of it doesn't seem to tighten up that well.  This seems like a recipie for disaster.  Toothpaste & other crud is going to stick to this area like crazy.

Am I doing something wrong?  Do I have the wrong part?  If so, what does the right part look like?  

This piece is plastic, and the piece that came out was metal but did not have a gasket on the backside.  Presumably they sealed it with caulk or plumber's putty?  Can I do that here?

This pic is with the nut on the backside as tight as I can get it by hand and part of a turn with a wrench.  Given that its plastic threads I am not inclined to use much more force than this.

The gasket goes on the bottom, under the nut.  You use plumbers putty on top, although its not really important, because the overflow feeds in under the chrome bit you have there.

I think the rubber gasket goes under the sink. I have no idea how it works, but it seems to for me. 

edit, beaten by someone who seems to understand it better than me!

There is a big rubber gasket on the bottom (BB).  There is a small one on the top (AA).

I use plumbers putty on the joint between the tailpiece flange and the sink drain.

https://www.thespruce.com/bathroom-sink-drain-installation-2718843

We always discard the rubber gasket for the top and use putty. As mentioned, it's not critical, but an eyesore is an eyesore.

One more vote for plumber's putty instead of a gasket on top.  Put a bead of it around the underside of the flange, tighten it down and wipe away the excess that squeezes out.

Thanks guys.

Like they said above, putty is the way to go. 

All the leaks I have fixed were from old dried plumbers putty. Decades old. I am not a plumber, I just help keep them employed...

I use silicone caulk for drains instead. Remove everything, calk around the drain hole recess what will be covered by chrome ring, drop in the drain then fit the nut. I do this now and don't get any leaks. I'm sure I will curse myself when it has to come apart if ever.

It's controversial, read up on it, but ditch the upper gasket anyways.

I feel the need to mention that the upper gasket, putty or silicone is only there to prevent water escaping into the overflow channel.  No external leak.  The way I use bathroom sinks, its entirely redundant.  Kitchen sink needs it.

Plumbers putty is trash and should be illegal. 

One other thing to note.  Make sure you run some silicone on top of the beveled washer and along the threads where the washer is going to finally sit.  Water can follow the threads and drip off the bottom of the p trap.  The silicone on top allows you to not have to tighten the nut super tight to get the washer to seal along the bottom of the sink.  Most of those pop up assemblies come in gray vinyl now.  You can tighten them really tight, but over the next couple of weeks, they will slowly stretch and then pop.  Trust me, too tight means failure two to three weeks out.  No, plumbers putty when properly used is awesome stuff.  Its not for sealing threads.  Its used to fill gaps with a material that will not harden. Even works great to seal things in the project cars.  I use it to seal the shifter cover to the tranny tunnel so that no fumes get inside.  Also works pretty well sealing up gaps in the firewall.

^Thanks.  I am going to take it apart and give that a shot tonight.  This morning I noticed its leaking right along the threads through the bottom washer.