It is dishwasher safe. I run mine through the dishwasher whenever I run it (which only happens when I've been lazy about dishes all week, since one person doesn't generate enough dishes to run the machine every day or every other day). The heat helps sterilize it. Open and remove lid, which I hook over a spike in the dishwasher with the flat side up (or else water pools in the lid).
Otherwise I wash by hand every few days with soap and hot water, and play with the nozzle to let some soapy water run through it. Then rinse thoroughly, play with nozzle some more. If it's already out, I'll run bleach through it too, but I'm usually too lazy for that step. I run lots of hot clean water through to make sure I don't have any soap left.
I like the nozzle for function, but don't like it for cleaning. It's pretty much impossible to clean regardless of method chosen. I like the wide opening - way better than traditional water bottles for cleaning.