Go to your backyard, get your water hose, put it on like jet spray, spray that mess down until it all falls to the ground. Then depending on the content of your sheets, what type of material it is, splash some bleach on there. If you don't have bleach in it, the bleach wouldn't work, then splash some strong vinegar on there. Let it sit for a couple of days, take it in, wash it. Don't care about the shame from your neighbors because you shouldn't have pooped in your sheets. That's your fault.