I'm a personal trainer with certifications in fitness nutrition (I'm not a dietitian, those are actual licensed medical practitioners you go to see about dietary needs. I can legally provide guidelines, but I can't prescribe meal plans.)

Our body is great at getting rid of toxins and waste products. It's almost as if we've evolved ways of dealing with such things. Anyone talking about "toxins" and "waste products" as if they're 'stuck' in your body is either very ignorant, or trying to sell you snake oil. Probably both. I've seen a lot of it, especially in my profession. People making up bullshit to sound knowledgeable and sell you something you don't need. And yeah, a lot of trainers are just as ignorant and just trying to sell you something you don't need.

EDIT: In case anyone wants to sink their teeth into the topic, there's a very good book I read as part of my course work, called "Nutrition, 6th Edition" by Dr. Paul Insel; Don Ross; Kimberley McMahon; Melissa Bernstein. It's all very well sourced and kept up to date as modern science catches up. Available on AA if you don't want to buy it.