Now, we shall make a tube, and add finishing details such as scratches and some color
Now lets work on the tube, for a start we shall make a selection for the place on where it will be allocated, a rectangle one should do the trick (don't forget to feather it)
The process will be almost the same as the making a hole in the texture, except that the shape is a rectangle, we are going to do this in order to make an effect where the tube seems to be inside the texture, and we shall shadow it with the burn tool set in color burn in highlights mode as well.
After this we shall start to shape up the tube, by using the Dodge tool, to make the highlight in order to provide shape, make it a large brush, but very soft, to make it a bit subtle, something around the itensity on the image below.
With a little smaller brush add another highlight, this time make it fade in the top because light wont get till that point much...
To give it even more shape, with the dodge tool again, set in midtones with a very small size, around half the opacity when it was set to highlights, and paint in it like in the image
Strengthen up the bigger highlight again.
Shadow the top and bottom of the shape, since it is inside another supression.
The tube is almost finished, not onto the supression where it is inserted, make the correct highlights with a small brush with the dodge tool again and there you go! BUT REMEMBER: There are loads of ways of approaching tubes, here's an image with some examples, and remember that the process is exactly the same as this one, except that I put some burns in the middle of the highlights. Here's an image of what I mean.