I too cowash a few times out of the week & shampoo either every week or every other week. I don't have any build up.
I co-wash 2-3 times a week. I shampoo every other week with a no-poo and once every 6 weeks with elucence moisture balance. To be honest, I do not get a lot of build up. The only reason I shampoo/no-poo is because I work out a lot and I use shea butter and oils on my hair daily so I know at some point my hair would enjoy a cleanse.
Big Chop: 9/2013 Hair Type: 4a Current Length: 1/2" Goals: Love my hair & Let it Grow
I currently have a short cut so I co-wash daily or every other day with the intent to clarify bi-weekly. Previously, when my hair was longer, I would wash my hair with a sulfate free shampoo on the weekend and occasionally co-wash mid week.