Do vampires pee

They do, as they drink stuff they need, they must get rid of the old stuff so they are new and the vampire stays healthy.

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If they eat food, then yes.

I don't know one that doesn't eat food.

No blood is their source of food, and only blood much like the vampire bat, http://en.wikipedia.org/wiki/Vampire_bat

However I'm not sure if they go to the toilet, as I'm sure their digestive system is different.

The bat makes a wound by biting, and then licks the blood. Whereas a vampire bites into a jugular vein, and sucks it out. Another key difference is that Vampires are not a species like the vampire bat is but rather a mutation caused by a virus, which is the best explanation I've been able to find, which also explains why vampires can't have children but are able to infect others with vampirism. I do not think that simply being bitten by one is enough to infect you, but you must drink vampiric tainted blood. Otherwise there would be millions of vampires by now.

-TheUnbeholden