How to clean out a spastic colon?

I eat a lot of fiber and drink alot of water and I do have a bowel movement every day but it's these thin long strips. If I miss one day of the heavy fiber cereal either i don't have a bm or it's a very small one consisting of pellets and clumps. Seems that my colon is full of dried up impacted fecal matter, how do i get rid of it? And to those that don't believe in the theory of colon cleansing, how exactly do you explain spastic constipation?