Quick PVC tube/kitchen plumbing question

Hi, I'm new to this forum, and was just wondering whether if someone could tell me what I should do?

The plumbing under the kitchen sink was dissembled then assembled, however I think something went missing, the problem I have at the moment is the fact that I can't make two PVC tubes attach to eachother tightly

This is my diagram of the 2 PVC tubes:



I think I lost a rubber ring or something that should go between them to make it water tight?

Sorry, I've never done any DIY before so I can't use any technical terms

Thanks

EDIT: Bigger image = http://img73.imageshack.us/my.php?image=plumbingbx2.png

A picture would be better...kind of hard to determine exactly what you have there.

IF the bigger one has a nut, there should also be a tapered washer underneath it that gets jammed against the smaller pipe as you tighten the nut. If it is not that, without a picture, can't help you. To assemble, you slide the nut on the smaller pipe, then the tapered washer with the taper towards the bigger pipe, then tighten the nut up on the threaded part. As you do that, the tapered washer get jammed in and seals things.