In a spray bottle that 1 gallon woudl last you all day. Look it up on dealmed. Boiling sanitizing, but does not sterilize. It requires an autoclave to sterilize.
For cleaning the tanks themselves, a spray bottle would work. However, I wouldn't trust a spray-application for getting into all of the little pores of lava rock or the driftwood. Regardless, I'd still be concerned about toxic chemicals remaining in the rocks and driftwood after I was done.
After doing a little reading, it seems that dry heat also works for sterilizing, which takes me back to the other option I mentioned of using the oven to bake these materials.