We have an adorable 12 week old beagle x staff who is settling in very nicely. Waits at the back door for number 2s and as long as you take him straight after nap/drink will wee outside too. But he'll also wee whenever and wherever he feels like it in the house to t. I mean 2 minutes after a massive wee outside, he'll go on the floor inside... It's driving me mad, he absolutely knows to go outside, holds it all night, but then just piddles as he feels like it, tiny dribbles usually 
Is this just a puppy thing? Any advice?!