Don't try and clean them, there's a chance they'll get blocked up by some microscopic crap. I was probably unlucky, but i managed to ruin one of mine once by wiping the nozzle with some clean diesel and a lint-free cloth... 
Ideally what you want is to remove them in a proper clean room and put them through a sonic bath, then immediately cap them and then store them in a container of fresh diesel. Obviously very few people have access to a clean room or sonic bath in reality, so the best you can do is plug the ports and seal them in a clean container of fresh diesel.
That said, it might not make much difference in practice, i'm just going on Bosch guidelines. For the sake of an extra five minutes to store them properly, can't hurt.
Ideally what you want is to remove them in a proper clean room and put them through a sonic bath, then immediately cap them and then store them in a container of fresh diesel. Obviously very few people have access to a clean room or sonic bath in reality, so the best you can do is plug the ports and seal them in a clean container of fresh diesel.
That said, it might not make much difference in practice, i'm just going on Bosch guidelines. For the sake of an extra five minutes to store them properly, can't hurt.