Please tell me, could a ct tap show bowel cancer?

Sometimes: I'm not sure what a "ct tap" is. I assume it's a typo for "ct scan". A ct scan of the abdomen and pelvis can sometimes show bowel cancer, but often they can be difficult to detect, particularly in the large bowel (though this is improved with dedicated ct colonography, which increases detection of colon cancers though may not find other diseases as well as a standard ct).