If at a dump station, I just dump and run. However, before I stick my rig into storage, I try to get a night at a FHU place so I can take my time and get the tanks readied for storage. I like taking some time and making sure the tanks are well rinsed.
I've seen some tanks come with a watertight access port. If my rig had that, I'd probably be going at the tanks with a wet/dry vac, perhaps making sure to clean the protruding sensors extra carefully. That way, I know there would be nothing in them that could cause smells or clogs when the rig goes into storage.
