@Wendy1975
My two cents worth:
Size matters, but for depth you probably need to start with something smaller. Personally, I like the Siliconenozzles CT-75 (1-inch tube). I have quite a collection of silicone nozzles. I like the slightly larger diameter because it is small enough to thread through but larger enough without much chance of folding over. A #18 firmness is my personal preference (I like translucent tubes), but as the tubes increase in diameter, I will go with a softer silicone. The tube is also large enough that I'm less concerned with perforating the colon.
I know my anatomy and know I have a "long" sigmoid (as in the length above the rectum is pretty long before making the turn to and up the descending colon). It's about 28 inches from my anus to the turn at the splenic flexure. The turn is complete by 32 inches and the nose of the tube is then threading through the transverse colon.
The hardest turn for my longest tubes to make is at the hepatic flexure. Apparently it is a really sharp turn for me. At more than 44 inches at this point, it can be areal challenge and if it doesn't look like the turn is going to be made, I'll stop at this point. When the turn "opens up," it's a pretty remarkable feeling. My longest tube in this diameter is 54 inches. But filling from this deep is a very different feeling from a more normal enema.
Retention: retention nozzles help but the enema solution (temperature, composition, volume) seems to matter as much. The closer you get to your maximum volume capacity, the shorter the hold time is likely to be. Half to two-thirds of your maximum will probably be the optimum volume. Temperature is best when warm, not hot. The enema solution I find the most easy to hold is baking soda.
A quick clean-out enema makes my subsequent enemas more pleasant.
For a bit more of a kick,I like shaved Ivory soap to be dissolved in the solution. It reminds me of the enemas my mom used to give me. With this type of enema solution, I go for the inflatable double balloon nozzle. For more of a kick, I use soap and glycerin but I really need the time to fully enjoy thsi type of enema (including rinse and a final calming baking soda enema). The inflatable nozzle can stretch your internals a fair amount to seal everything in. But if I really want a seal, I have some pretty big silicone retention nozzles. They do a good job of sealing AND there is no mistaking that there is a very firm and large nozzle sealing me up.
Lube: a good water soluble lube is my favorite. The generic store version is fine. The best one I've found is "Fuck Water" (look it up on Amazon). Thinner and very slippery. Don't use silicone lubes on silicone nozzles. Petroleum jellies can be tough on certain softer flexible polymers. I also use the powdered J-Lube. Just wet and spread. Lasts a really longtime. You can also mix it up to make your own liquid lube, but it takes some time to do that correctly.
I think I've contributed my thoughts to questions.
Welcome to Zity. Hopefully, you'll find those of us who post publicly are not "jerks."