When dogs scoot their butt on the floor. It is usually their anal glands. Their anal glands are at the 5 and 7 o'clock position in the butt. They usually express when they have a bowl movement. But not all dogs are able to express them, themselves. So usually your vet will do it or groomer or you could learn to do it yourself. They can get infected too. I express my one dogs anal glands she is the only one that seems to have this problem. The fluid that is in those glands is very stinky. Hope that helps.
Wendy@newyorkies.net