I've had the same thing on my fish for hours or days at a time. I doubt you'd see a parasite that big on a fish. Most parasites are microscopic, or basely visible to the human eye (e.g. "Ich"). I think it is, as you suspect, waste. Some fish just never seem to get rid of it. Doesn't bother them, though!
If you look at your fish mostly when you're feeding them, this may accentuate the phenomenon in your eyes, since this is when their digestive systems are most active.
As to the red color. If you feed your fish a colored flake food (which most ppl do), then the waste can also be colored! I certainly see that with my head-and-tail-light tetras all the time.
I wouldn't worry too much. Let's see what others say, though....
is a blessing, not a disease.