Not sure what happened to knocking, but seems the professor wanted to be sure Martin wasn't cheating, even though she knows full well he doesn't need to. He couldn't care less if she watches, it's only awkward for her…

Martin can't just produce infinite amounts of cum, but his first couple of loads in a row are pretty massive for a Sylveon. In fact his ejaculations tend to be about as big as his body can drive out of him, so he can't physically blow bigger loads naturally. Though after the first two or sometimes three they drop by off very fast, the next being only about half the previous, and then the following being much less. Though this is only if he's just blowing one after another, pacing himself he can probably get off a full load every three-ish hours provided he stays hydrated.

Being pent up is also a very physical thing for him, he can feel the volume built up, and one release might not be enough every time. Sometimes he wakes up in the morning feeling like he's been edging the whole night, if he hasn't been properly spent the night before. This all makes him more than a competent breeder, if not absolutely overkill, even if his partner can handle his size.

This was another spontaneous image, and I think I drew Martin's junk a bit on the large side this time, but there's also perspective going on, so I'm actually not sure.