I took a portion of my kitchen sink pipes apart today to unclog one of them and THINK I put them back together just the way I found them. I had a problem with the end of the "J" bend (not the top) but got it mostly corrected. The bend does not appear to leak at the time I run water but, if I come back and check later, there is about 2 oz. of water in a bowl I have under the "J" bend. Any suggestions?

I am assuming your talking about drainage since you use the word unclog, but I would have to know what you mean by "J bend". On a kitchen sink you would have a "tail peice" coming off the drain in the bowl, connected to a "p-trap" or if you have a dish washer or a two compartment sink, a combination of a "p-trap" and a "sanitary tee" (or "san-t") to complete what is called a "continuos waste" system. I have attached a picture of a "p-trap". The "p-trap" would be the only thing holding water and leaking while the sink was not in operation, so that must be what you mean by "J bend". This may be as easy as tightening the compression joint connecting the two pipes, but if you forgot to put the compression ring back in the joint (a common mistake made even by plumbers) this will do nothing to fix the leak. The compression ring is usually a black rubber ring or a neoprene plastic ring in a sort of wedge shape. Check for the ring, if it is there, make sure it is clean and put the joint back together. Tighten hand tight. This should fix the leak, if not, give it a 1/2 or 3/4 turn with a spud wrench or large crescent wrench (both available at home depot or lowes). I hope this helps.

I would have to know what you mean by "J bend". I'm amazed that after the great answer Fish posted, (and it was top notch) that he would ask that question. A "P" trap comes in two pices. A "J" Bend, The curvy piece, and the "trap tail" that goes into the wall.
Follow Fishes advice! Good answer Fish! Tom