I googled "how to stop my dad from stuffing toilet paper down the sink" and found an old discussion on here. Come to find out, toilet paper obsessions are not uncommon. I did want to put in a couple bits of advice as I had seen people having issues with overflowing toilets. My dad has Alzheimer's and I care for him at home. He has had an obsession with toilet paper, paper napkins, tissues, for many years now. It started with tissues, so I hid them. It moved to paper towels then to napkins - had to hide those. Toilet paper is a little tougher as it needs to be around for him to use. He also had an issue with flushing the toilet several times in a row which made it overflow. About the third time of doing this, He overflowed it so bad that it went through the floor and flooded the basement with about 1/2 inch of water. It only took a few minutes for that to happen. After that, I had a plumber come and install two, no overflow toilets in the two bathrooms he uses (1 upstairs and 1 downstairs). The toilets were not expensive - about $160 each at home depot - it was the installation that cost me, but if you have someone that can do that for you, it is a reasonable fix. I have not had to unclog a toilet since the new toilets were installed and there has been no overflow issues !! Now for the past couple of months, he has been clogging the sink with used toilet paper and food. I have tried putting a screen drain but I cannot get it to stay. I have finagled a shower caddie that was nylon with holes all over and tied that in so he couldn't move it, but that did not work so well. Last night he flooded the bathroom and it went through the floor to the basement, again, because the sink was clogged and he ran the water until it was everywhere... so I did turn off the water at the sink until I can figure something else out. I did not want to have to cement the strainer into the sink ( I wanted to be able to remove it for cleaning purposes) but now I am thinking I need to cement it in so he cannot remove it to shove stuff down there.
can you change the faucet to one of the infrared ones that will shut off once the hand it removed from under the faucet.
Or there are faucets that you push down the handle and they go off automatically. You see them in commercial places particularly schools and Day Care Centers.
But neither will prevent the pipes from getting clogged if he is putting food and or towels down the drain.
It all comes down to monitoring him while he is in the bathroom. Just another part of the decline.