Poopy diapers don't really bother me!
Everyone poops.... I also don't think its a huge deal that he's four and still poops in his pull up. Is it all the time, or was it a slip up? Does it happen when he's nervous?
I remember when I used to have exams for school... I would always get what I like to call "Sick bum", and I was 25 and still thought I might crap my pants! Maybe its a nervous thing! Maybe its a parenting issue, maybe he's just not ready...??
Just put your gloves on, hold your breath, say a little prayer, and go as fast as you can! I have a girl who uses cloth diapers.. I not only have to change her, but I then have to clean our her diaper. It's not a big thing for me though.. I have a high gross tolerance!