The vet should be able to get the feces if you just bring in the snake. Admittedly, it's a little alarming to watch someone treat your snake like a tube of toothpaste, but it's pretty easy to get it out that way--and it's better to have a really fresh sample, because some parasites are in the feces, while others live in the surrounding fluid. So it's difficult to diagnose, say, flagellates with a two-day old dry sample of poop. (And flagellates are one of the few really common parasites for captive-bred ball pythons.)

But before you take him to the vet, it's worth feeling Xander's lower body to make sure he actually HAS something ready to go in his lower intestines. One time I brought in a female that was so empty, the vet couldn't safely extract a sample--so I had to go home, wait two weeks, and bring her back when she'd done a bit more digesting.