According to a panel at Writercon II, yes, they do. This was opinion, however; it’s never been canonically established either way.
We do know that vampires are capable of ingesting things that carry no nutritional value — Spike was seen enjoying liquor and hot wings, and seemed to approve of the blooming onion — and, if he took in stuff that his body couldn’t convert to energy, it had to go somewhere, didn’t it? On the other hand, vampires are explicitly supernatural creatures, so we can’t assume with total confidence that any particular natural law applies to them.
My own thought is that, since blood is all they need for nourishment, nothing gets excreted; any other liquid might very well be eliminated through the former human urinary system, still in place but useless for any other purpose.
Final answer: you can run it either way. Just provide an internal argument in support of your choice.
no subject
We do know that vampires are capable of ingesting things that carry no nutritional value — Spike was seen enjoying liquor and hot wings, and seemed to approve of the blooming onion — and, if he took in stuff that his body couldn’t convert to energy, it had to go somewhere, didn’t it? On the other hand, vampires are explicitly supernatural creatures, so we can’t assume with total confidence that any particular natural law applies to them.
My own thought is that, since blood is all they need for nourishment, nothing gets excreted; any other liquid might very well be eliminated through the former human urinary system, still in place but useless for any other purpose.
Final answer: you can run it either way. Just provide an internal argument in support of your choice.