I just did a version of the deep cleaning mentioned in the archives. I didn't have tea tree oil (used lavender oil instead), and no lemon juice, but still... gah. I keep my hair pretty clean but was grossed out at all the dark water running from my head. I just did it in the shower and let the baking soda / salt / lavender oil / warm water soak for a few minutes and then just rinsed it out with apple cider vinegar.
From now on I'm doing it regularly. My head feels so light and clean now :)