Getting back to the original question @chefbv had,
What is the value of a colon tube?
1. Colon tubes are more fun than practical. You get some nice sensations inserting them and using them. It also puts you in an almost surreal state of mind, a perverse psychological high, or 'mind fuck' as I like to call it, when you experience getting something really deep into your body. I like urethral sounding for the same reason. It's probably what drives deep throaters and sword swallowers too, (no experience)
2. Colon tubes make high volume enemas easier by reducing the urge to expel during an enema. The theory is that deep injection avoids stimulating the sensitive nerves in the rectum, inner sphincter, and bottom of the sigmoid that often trigger expulsion reflexes. This works in my experience.
HOWEVER, a 12-inch retention nozzle is just as good at reducing expulsion reflexes, I think.
3. Colon tubes inserted deep in the colon are probably the best way to wash out the final 10% of solids if you want to get as clean and empty as possible. Everything is always flowing out and washing out in the same direction. Unless you've been fasting for a day or two, however, these benefits are only transient. Your ileocecal valve could suddenly open, as it does every few hours, and dump a new batch of goop into your ascending colon.
A fun thing to do is leave the colon tube in and get a continuous inside-out flow going for however long you like. ProV1 has a rig he can use to keep his bag full with a hose going into his bag that he controls while his enema is in progress. I've done it by hooking up my tube inside me to my shower shot with the diversion valve set to deliver low flow rate of a under a gallon per minute.
If your primary goal is getting the whole colon clean and empty fast, I have these two nozzle recommendations. Get: (1) a soft silicone retention plug as large as you can insert quickly; (2) a 12 inch retention nozzle designed to go a few inches into the sigmoid that has a large retention ball to seal the rectum just above the anus. I'd go with at least a 1.5-inch diameter nozzle with at least a 2" retention ball in a medium soft material that has some stiffness but is still fairly flexible.
The fastest way to the clean and empty goal that I've found is to use the retention plug on my first gallon bag, and switch to my 12-inch retention nozzle for 3 or 4 more gallon bags. If it's been a few days since my last deep cleaning, I may need do two gallon bags with the retention plug before I can insert the 12-inch retention nozzle.
12-inch retention nozzles are great. If you've never experienced getting something 1.5" diameter or wider through your inner sphincter into your sigmoid, you're in for a treat. Don't force in the nozzle. Lube it really well, get really relaxed, run a slow flow of warm water through it, as you ease it into your rectum. Push it in until it hits resistance at the top of your rectum. Then work it in and out to prod your inner sphincter. You might need to aim a little backward toward your tailbone. The warm water and gentle prodding should start giving you a really good feeling up there as your sphincter relaxes and starts to open up. You may feel like you want to go deeper. Go ahead. That good feeling is the signal to gradually prod a little harder and deeper. It should feel better and better, never painful, as your nozzle opens up your sphincter until resistance gives way and you push into your sigmoid. That should feel great. Slowly push the nozzle in all the way, which should only produce anal resistance as the retention ball pushes through your anus and seats just above it to lock your nozzle in place. The nozzle should now feel totally wonderful inside you. Go ahead and masturbate if you have to. Now you're ready to open up your valve all the way to enjoy a gallon going in easily and effortlessly with no hands, no leaks, and no urge to expel, (at least for most of the gallon bag.)