Bringing in dirty diaper

My son's doctor wants me to bring in a dirty diaper so she can get an idea of his poop since he isn't pooping frequently. His poop is soupy and it's a lot since he only poops every couple days therefore it's always a massacre. I can't get a "clean" dirty diaper and I don't want to take a messy dirty diaper and have them looking at me like I'm crazy lol. Any suggestions? Anyone had to do this?