IIRC from a podcast interview with one of the founders, you swab a bit of your used toilet paper for the gut sample collection.

The concept sounded pretty interesting, and it's on my list of things to do this year along with 23andme. Gut biome health is getting more awareness these days, and with them comparing large populations of samples it seems like a cool way to contribute to a data set that ought to provide some useful insights.

I was reading a post recently about someone who had surgery to remove part of their intestine due to some sort of GI disorder, and wondered how many of these sorts of major procedures could ultimately be avoided using biome-based treatments like fecal transplants.