The question is, once the cat is in the trap, what will you do with it? Not seeking revenge for it's toilet habits I hope. It is most likely neglected and knows no better. Find a certain time the cat comes, then get a good look at it. Bait it with food and bring it inside, then call the ASPCA. Pet it and be nice to it, it likely has no home.
Go to your local Animal Control and get a small animal trap. Hide it by your door with some food in it. Once inside you can bring to animal control for adoption. It's obviously an intact male that needs a neuter!! They can help!!