I have just seen this thread.

The problem Sguur mentioned is called an ectopic ureta. If you googel you'll find loads of info. It can be the cause of UTI's or can be mistaken for a UTI. It can cause frequent urination or a constant dribble of urine, meaning the dog will smell and the skin at the back end can become burnt.

My friend had a litter of pups and one had an ectopic ureta. Luckily my friend noticed somethign wrong at 3 week sold, as the pups back end was always wet, and the vet initially thought it was a urine infection. The vet did say it is often missed until the puppy is much older. Anyway, pup had tests to confirm and was operated on at about 6-7 months old. Op was successful and puppy is now totally dry and normal.