Personally, I just can't stand the idea of spreading any kind of bowel bacteria. So I try to get as much fecal matter as possible off by swishing in the toilet (I also flush when I'm holding them in there to get a clean water rinse). Then transfer from the bowl to a bucket with lysol for a 1/2 hour or so, and into the washer (by themselves) for a hot wash and double rinse.
For undies with just urine (which is sterile), I just rinse a few times and then throw in with the regular laundry.
-Ivy
Parenting two active, wonderful boys
This is your world. Shape it or someone else will. -Gary Lew