Why does my lab poo and pee in his kennel at night?

Despite that he is a young adult, probably the best way to handle this is to train him as if he was a puppy. That means getting him on a consistent schedule where you feed them at the same times daily & walk after meals and every few hours, and before bedtime (and you may need to offer a quick opportunity for relief overnight) . Initially, this might mean that you walk to a potty spot (not necessarily a long walk) every 4-6 hours and give lots of praise every time dog relieves itself outside. I would suspect that this will be remedied/solved by being on a consistent schedule and any nervous anxieties the dog has being calmed. Oh, and use a good enzymatic cleaner on anything soiled. Nature’s Miracle is highly regarded. If you are consistently offering frequent opportunities, first thing in the morning, last thing before bedtime, (maybe once overnight) and throughout the day, and this continues, you might need to visit a vet to make sure there’s no medical issues causing this.