Where do I pick up the Colosseum Underground Tour

When you get to the colosseum there will be three lines to get in. Just go to the center line and use your romapass. Then just follow the signs for the tour. It's very easy. Be sure to get there at least 15 minutes early. Donna

Thanks for the answer, however I'm still a little bit confused. Are the 3 lines after going thru the initial security line - or are there actually 3 security lines waiting to get in initially?
With my tour being at 1pm is allowing 15 minutes going to be enough time to get thru all the lines?

There are three lines to get in. The left line is for tour groups, the center for romapass and pre-paid entry tickets and the right is for people buying tickets. I would get there no later than 15 minutes early, preferably half an hour early. This way if there is a line up you'll have time to get through it and if not, you'll have a few minutes to look around. Donna

Get them as early as you can. I think they were open at 8 or 9, we got the tickets, then went to the forum and came back for a later tour. Our experience in Italy is that things are always slightly chaotic, and when we picked up our tickets for an afternoon tour, we had to stand in the same lines as the tour guides, plus, they have to find you and your # in the computer, and then sift through a stack of paper to give you the stickers you have to wear for the tour; which brings up another issue: they don't stick very well or long.
Last week one of the couples' on the tour had lost their stickers, and said it was very difficult to convince the cashiers to replace them! From our experience last week, 15 minutes is barely enough time if at all, and they do leave at the time stated for the tour as they are pretty tightly set; English, Italian, German, and so forth, one on the heels of another. The tour does last between 65 and 70 minutes so you will have time for pictures and questions.