Definitely a biological washing powder solution, it kills off the 'fats' that keep the smell so strong. Such a terrible pong, I can never understand why people grow flowering currant which smells very similar!
I think people who keep their tom cats 'whole' need to come and smell what they do in other people's houses. Our neighbour had a tom, we had two girls (spayed), and we suffered terribly with him spraying and night time fighting, she threw him out all night. When I told her he'd yet again sprayed up my curtains she said 'he never does it in our house'. That's the point, he does it everywhere else, especially where there are female cats. He regularly sprayed our front door, came in the cat flap into the house and sprayed up the corners of the room, it was dreadful. The final straw was when he pee'd on my pillow. I went to see her and she agreed I could take him to the vets, I was a cat protection volunteer at the time, and had him done. He lived a much happier and longer life.