I fill with clean water, add a drop or two of dish soap. Shank for 10-20 seconds, then let it sit on the counter for however long it takes me to get back to. Then rinses out a bunch until I know for sure the soap is out. I've never had a problem getting sick or having any weird tastes in my bladders.
I've also thrown them in the freezer as well after they've been cleaned, but not always.