I've had somewhere around 25 colonoscopies over the past 35 years - I have a particular combination of maladies that put me at extreme risk of colon cancer, so I've had to get them as often as every six months (though I'm thankfully back down to only once a year).
During all this, I've had most of the preps that are out there at some point or another. How the prep affects you is somewhat individual, so all I can do is describe how they go for me.
The easiest for me is Miralax/Gatorade - typically 238 mg (14 doses) in 2 quarts of Gatorade. It's normally done as a split prep these days because studies have shown that it works better, but if you're fecal incontinent you might ask your doctor about not doing it as a split prep. The split prep is basically that you drink half at 5 PM the evening before, which generally kicks in around 6:30 (for me, anyway - that's one of those things that's highly individual) and keeps me in the bathroom for around an hour. Then you drink the second half eight hours before the procedure (usually in the wee hours of the morning), wait until you're done on the toilet (another two and a half hours for me) then back to bed if you can. I don't normally have fecal incontinence, but it's not unusual for me to have leakage any time between when I start the prep at 5 PM and a few hours after the procedure.
The non-split prep likewise starts at 5 PM, but you drink the whole thing (it's not all at once - an eight ounce glass every ten minutes until it's gone) and it keeps you on the toilet for a bit longer (until 9:00 or so for me), but once you're done you're done. I tend to have a bit less leakage with this sort of prep, but it's still enough of a problem that I'm prepared for it.
The prep I tend to request these days is Golytely, which requires a far larger volume (4 liters) and is foul tasting (it has salts to help prevent unbalancing your electrolytes) but does a far more reliable job of cleaning me out fully, maximizing the chance of a good exam (which may be lifesaving) and minimizing the chance that I'll have to get another one done because of a poor prep. It's the same drill, a glass every ten minutes until it's gone. It can create nausea and feelings of bloating, but I put up with that as the price of a good prep. My secret weapon with Golytely is an IMMEDIATE rinse of my mouth after each glass - I have the prep in a glass in one hand and clear water to swish around in my mouth in the other hand, so I can get the taste of the salts out of my mouth as soon as possible. That cuts down on the nausea and makes drinking the whole gallon plus a little easier. I also use an antinausea medication (ondansetron/Zofran) beforehand to help keep the nausea at bay. Lately I do this as a split prep, so I start at 5 PM and finish the first half at 6:10. The diarrhea usually starts between 6 and 6:30, and I'm done by around 8. Then I get up eight hours before my appointment time and do the same thing - for the colonoscopy I have scheduled for next month, I got the appointment as 8:00 so I'll start the prep at midnight and be in bed around 3 AM.
Whichever prep you use, make sure you use liberal amounts of a skin barrier or Vaseline on your bottom, and reapply it each time you wipe. That largely prevents the burn that made my first few preps so unpleasant. The first prep I had was when I was 19 and living in a dorm, and I didn't know to get something softer than the John Wayne toilet paper that the college provided - OUCH! I also didn't know to wear a diaper after the prep started, leading to more than a little embarrassment in front of my roommate, though he was a real trooper with it, and never complained about my monopolizing the bathroom for the evening either.
Honestly, the worst part of the prep for me is that I have to be on a clear liquid diet for two days beforehand (used to be one day, and I'm not sure why that changed) and there's something uniquely unsatisfying about eating nothing but broth and green or blue Jello. The prep itself is unpleasant, but it's over quickly. The colonoscopy is absolutely nothing - they used to use Versed on me, which I seem to have a fairly high tolerance for so I'd remember the whole thing, but lately they just give me propofol and I'm completely out until suddenly I'm not, and the procedure is done.
My last colonoscopy, and my next one as well, have been chromoendoscopies, where they use a blue dye to stain the lining of my colon to try to highlight dysplasia amongst all the scars from 35 years of colitis. That's interesting in that it makes me pee blue for a few days afterwards, and last time led to the worst post-colonoscopy bowel accident I've ever had. That last may also be due to the very large number of biopsies they take each time (84 on my last one), hoping to find flat lesions before they grow into something serious. That has a lot to do with the specific conditions I have; most people don't have the same risk factors, and don't need all the extra steps and all the biopsies.
For most people, colonoscopy is a day or two of unpleasantness followed by a procedure that you won't even remember, and it's well worth it to find problems before they become serious.
