Generally speaking, a little bit of self-exploration will answer that question for you better than anyone else can.
To the other, it's also a matter of how you define dirty.
(1) The body produces natural rectal lubrication; it's not necessarily sufficient for intercourse, which is why there is such a breathtaking range of lubricants specialized for anal sex. Still, though, the point is that the body produces a natural lubricant.
(2) I think I'm safe in saying most guys, when we learn to admire and desire the concept of a "wet" woman don't really understand what we're dealing with. The lubricant effect is an evolutionary result, to be certain, but it's primarily―as in, its most common day to day purpose―a cleansing fluid, essentially removing perceived pollution.
→ When you stop and think about it, sure. But, you know, I admit it never occurred to me to think of it that way until the nice ladies from I forget which organization were explaining it to our daughters during the joint portion of the family menstrual training seminar, which term probably overstates the evening, but it's true I went to two different classes to learn how to deal with the fact that I was a father about to be giving a young woman advice on the whys and hows of her body's cycles and the effects thereof.
→ Whatever, I'm just trying to not say, "vagina snot", because that's (A) disgusting, (B) not quite right, and (C) most likely unwelcome among women who are probably tired of hearing it. At any rate, sorry, ladies; I just need that point, because―
(3) ―it seems worth noting (no, it doesn't, but, you know, whatever) I'm pretty sure that while
c + r > n, and
c > n, so also is
r > n.
→More specifically, I've had my tongue in more sunless places than noses. By far. Jus' sayin'.
Or, rather, something goes here about how we define dirty.