The forceful, sometimes violent expulsion of liquid shit into the toilet at high velocity. The "spray paint" term relates to the viewing of the underside of the toilet seat and the general condition of the toilet bowl which is usually well sprayed with dumpage.
"Man, I had such a gutcramp, I ran to the bathroom and let go with spray paint. Damn, it's a good thing we're at Frank's house. I wouldn't want to clean that up at my house."