The 3 day method is Lora Jensens 3 day potty training http://www.3daypottytraining.com/
I had a daycare client parent approach me about this a few years ago. I was game if she was. She had to do the initial stuff. I always hated the mention of toilet training until this. Now its the go to method I push parents to do and in the last few years ALL of my daycare kids have been trained with the method. Ages 22 months to 28 months. ALL succesful. Sometimes poo comes along later as fully successful, but mostly its a done deal all around.
My great neice did this over this past weekend. She turned 22 months on Monday. The first day was HELL. then at 10 pm, with mommy sleeping on the floor next to her bed....little K woke up going MOMMY POTTY..and from that point on, NO accidents.
You set aside 3-4 days. No ERRANDS..you do not leave the house. No housework, no big tasks. Have easy meals to do, no distractions. Stay totally microfocused on the child the whole time. No big football games, or shows to catch. Nothing. Its vital really.
And you leave the potty in the bathroom. Why anyone allows a child to pee in the living room or kitchen is totally beyond me! Just my opinion. But encouraged in this literature as well. And you never make a child go potty. Never make them sit on the toilet. They are in charge. You use constant (almost harrasing..LOL) statements. "I can help you go potty" "remember to let me know when you need to go potty" "I am here to help you go potty"...never a question "do you need to go pee", etc. They will usually say NO, then pee on the floor.
I also did ONE M&M for a success..none for a try. You had to produce something to get the treat.
I know many are nay-sayers about how a 24 month old can do this, but they do. Kids are capable of far more than most adults give them credit for. I see it everyday and know dozens of kids who have been very successfully trained this way. It is hard...the first day can be hell..even into the second, but it does "click" and success follows.
Good luck!