Be honest: when was the last time you cleaned this, if ever?
De-gunk it: Remove the knives, then turn the block upside down to shake out crumbs. (You can also use a can of compressed air, like a computer keyboard cleaner.) Wash the block in hot soapy water and get in the slots with a small brush, like the kind designed to clean baby bottle nipples. To sanitize, soak the block in a mixture of one gallon of lukewarm tap water and 1 tablespoon of 5.25 percent household bleach, or just fill the knife slots with the mixture. Let it sit for one minute, then rinse thoroughly with clean tap water and place upside down to dry. Avoid germ buildup by washing knives and letting them dry completely before you put them back in the block.
What to do when your phone falls in the toilet. (Because it’s going to happen at some point.)