I assume this is a sewer pipe right?
And are you planning to go for a abandon one or a still in use one?
If still in use, i would say include some of that nasty water and some moss.
If abandon, i would add more wildlife to the picture to make it feel like its not in used for a long time. Some dried water spots or something as well.
if there's any suggestions on what to add, that'd be awesome!