I make my own peanut butter and it is not that hard to wash out. I just grind dry roasted peanuts in my Vitamix (nothing added) and put the fresh peanut butter in two small jars. They stay fresher that way and I like my pb a little crunchier than DD & DH, who like it SUPER smooth. I run the jars through the dishwasher along with other dishes and they come out sparkling clean and ready for a new batch.
Cleaning the Vitamix after making pb is a bit more challenging than the usual cleaning routine. I add a bit more water and a drop or two more soap and I run the Vitamix on high longer than usual. Then, I actually use a rag inside the container with the hot dishwater. It rinses clean after that. (I don't usually need a rag or any manual cleaning efforts with my Vitamix.)
On the rare occasion we buy pb in plastic containers (group camping, large picnics), I don't wash those out to recycle due to all the gunk and how long it took me the one time I did do it. I wasted a ton of water to recycle that one plastic jar.