What is the best way to put a dog down at home?

My cousins dog is 16 years old and has recently had a lot of problems.I believe it has diabetes and his sight might have suffered as well.Unfortunately we already spent all our money on a taxidermist and I can't find any vets in the area that will do it for free.Then it hit me.Vets are just a bunch of greedy *** holes that would rather get paid then put a suffering dog out of it's misery.I understand you have to make a living but refusing to put a dog that is obviously in a good deal of pain out of its misery is just shameful.What are some good and relatively painless way to put the dog down at his house?