You sould pack the bearings with whatever grease you like. Waterproof grease is fine, though it's not necessary.
If you have a cartridge BB then the only maintenance you can performis to replace the entire cartridge. Replacements are generally pretty cheap so it's not worth freting over. If you think it may be going bad, just buy a new one of the same size (it should be stamped on the cartrdge) and replace it.