I would like to suggest that you do not even try this. It sounds as if you have had this animal friend for a long time and I believe that you owe this dog a humane ending to it's life. If this was me, I would find a vet that will come to your home to euthanize your animal companion. Yes, it will cost some money and your dog is worth it. You may have to make payments to the vet to have this done. Please give this last gift to your faithful, loving animal. It is the least you can do.