I do what MadnNatsmom does - "wash" my hair and scalp using conditioner only. I do a full shampoo every second day, then on the days in between and after workouts I just use conditioner. It actually does a good job of cleaning dirt and sweat off my skin. (I think it's similar to the principles of cleaning your skin with cold cream or olive oil, as ladies used to do 50 years ago - the oils in the product lift away the dirt on your skin without drying it.) My hair looks just-washed, my colour doesn't fade between appointments, and I don't get breakouts around my hairline or on my scalp. My hairbrush doesn't get dirty or stinky. I work the conditioner in very thoroughly, and I also make sure to rinse completely.
Note - I have always been a fairly oily-skinned person, and at 49 I still have definite combination skin. I used to be a 2X/day shampooer, so changing over a couple of years ago to what I do now was very difficult for me and went against my grain. I was truly shocked at how clean I could get my hair without using shampoo.
Stebby