It varies on quality of the food, how much is fed and how often that will determine how much waste they produce and when. They tend not to go a whole lot, not like goldfish or other ones you see who seem to always have poop dangling from them. But they should go a couple times a day at least.
The waste tends to be of a brown color- sometimes with a red tint if you use food that has a lot of dye in it (the food that "claims" to "enhance" colors).
If constipated you will notice other symptoms, such as a little more difficulty in swimming. Parasites you will see the waste as long, white and stringy.
Otherwise, a stumpy brownish small worm like (sometimes they are small round ball-like as well).. thing.. right before the large anal fin.