Moen 131553 Pop-Up Drain Assembly Kit

I installed a 131553BN sink drain about a month ago and tested it afterward for leaks. No leaking observed at that point, but we weren't actually using the sink until we had family in for the holidays. It was used a lot and I found that the drain was leaking badly. I had left a plastic bowlbeneath the drain when I first tested it, and it was full, with water dripping onto our new vanity and floor. I remember at the time of installation, that I was confused as to whether or not to use plumbers putty or silicone. I seem to recall reading that neither was required, so I didn't use any. When I looked at the leaking drain, it did look like the leak was coming from the area where the sink and drain meet. What should I do? Maybe just tighten it more? Re-do it with plumbers putty? And why does the drain tube barely reach the rest of the plumbing? Maybe this has some effect on the problem as well?