How to house-train your dog
Almost all puppy mill dogs have urination and bowel movement accidents in their new home. To a puppy mill dog, it's not an accident at all, to them, this is completely normal behavior.
Dogs in puppy mills are not expected nor are they taught, to go at any certain time or place. The concept of "holding it" is a completely foreign idea to them. To make matters even worse, most of these dogs are fearful of anything, which makes training hard because even the most positive training techniques can be fearful to them.
For puppy mill dogs, the basic rule is:
REWARD THE GOOD, DISTRACT FROM THE BAD. "Distract" meaning directing their attention away from the undesirable behavior.
Make sure you, again, be patient. You're teaching a dog to basically change a life habit.