Echoing what others say, you need a top down element.
Also I had my first colonoscopy about a month ago and my ADHD hyperfixated so I had an amazing prep, even had fun with it. Also I'll note my ADHD medication tends to constipate me so I had to deal with that too. Here's what I did. My procedure was Wednesday afternoon.
Four days prior I went on a low residue diet, basically no food with fiber.
Monday I did a mini prep. I used a 7 day supply of Miralax, two LMNT packets, and a slushy machine. I drank 8oz of Mira-Slush every 15 minutes. Got fairly clear by the time I was done.
Tuesday clear liquids all day. I drank 8oz of water every 30 minutes, every other hour I switched to a quart of water with one packet of LMNT.
11:00 AM Mixed a 30 day supply of Miralax and 8 LMNT packets into one gallon of water, placed in my fridge
2:00 PM poured one quart of Miralax mix into my slushy machine
3:00 PM I took four 5mg doculax pills
4:00 PM Drank one bottle of magnesium citrate (did this at the end of my therapy session in front of my therapist)
4:30 PM Started on Miralax, 8oz every 15 minutes which alternated between a slushy and warm water with it.
5:45 PM I paused because I was feeling full, resumed at 6:00 PM
I got clear that night, my diarrhea was never out of control. I laid in bed and caught up on reading and journaling. I resumed the next morning.
6:40 AM Took one Gas X with 8oz of Miralax mix, I then drank four more doses every ten minutes after this.
8:00 AM Took one Gas X
10:40 I went NPO
11:30: Wife gave me a 2.5 quart water enema, held it for 20 minutes as she massaged it into my cecum
12:30 I'm at the hospital, called back ten minutes later.
1:25 Scope gets inserted and I watch it all live
My GI said I had one of the best bowel preps she had ever seen.