Anyone who has any experience with one knows: Vaginas have liquid coming out of them. This is especially true if the owner of a vagina is having sex. Depending on the person, there will at least be some of the liquid coming out of the vagina at some point in the process. Some kind of absorbent padding will almost always be helpful in preventing stains. This is especially important if you think there will be some ejaculation, squirting, peeing, or period blood coming out at any point.
I made this mistake a long time ago when I fingered a woman on her period and got so much blood everywhere when she squirted that it soaked through the sheets and into the mattress, which required bleach to soak into it overnight.
Put something down to absorb it even if you don’t think anything will come out. Something might when you least expect it, so be ready for the flood.
That’s a true mess to avoid, but can I recommend a water and dust mitre proof mattress pad/topper?
Stuff happens, regardless of whether you wear a vagina, and mattresses are expensive. A water-proof mattress pad/topper protects your investment. A dust mite proof mattress pad/topper might reduce your allergy symptoms, which is a good investment in your well being. Don’t skimp on the mattress pad!