I see loong dildos like this and this sometimes and I'm always curious: how does it actually go inside of you? To get technical, does it coil up in the rectum or does it start going into colon/sigmoid territory?
Yep they go all up inside you, passed the sigmoid and into the large intestine proper. Training to open the sigmoid is interesting, takes you relaxing, listening to your body, and poppers help massively. You also need to learn how to deep clean, which is a bit of a challenge itself. However, when you do achieve all of that and have 3 feet of dildo all the way up you, my god it feels good. There's nerve clusters at different points in your large intestine that these things reach and it feels amazing to trigger them. They're not for everyone, but if you're into it, it's well worth trying.
I know a bunch of people who do depth play without poppers, they're not required. I'm not a depth play person but I have some toys which are long enough to poke into my sigmoid. It's fun and good
I've never personally used them but the intent is for them to go deeply inside you and not coil up in the rectum. Anything deeper than like 6-8" and you need to actively train yourself to take it, which is the purpose of the first set you linked.