Father-in-law keeps chopping up his poop so as not to clog drain! How do I get him to stop?

Asked to stop several times by different fam members, it won't stop! My husband and I moved in with his father over a year ago. Bill, the father in law, continues this practice irregardless of how many times I remind him of the health dangers! He just turned 94, still drives. But he is very stubborn. I am at my wits end. He takes whatever he uses to chop the poop and puts it in the linen closet, dripping the water all the way! We threw away the saw (yes!) and the spade he was using in the different bathrooms. (there are two) We have a cat and I'm sure it walks through the pathways he makes with the device. I just caught (by listening) him using a knife sharpening device with a wooden handle this morning in the upstairs bathroom. We thought he had quit! I just casually asked him when he exited the bathroom, "So what are you using these days to chop your poop?" He showed me the knife sharpening device that he had put in the linen closet! There are so many diseases! He drinks prune juice every day so I don't see why he has to chop his poop! I am SO worried I am going to contract a disease!