not either of these anons but I've thought about putting laxatives in my sister's drink before. I had it all planned out, with a small audio device ready to be hidden in the bathroom, and a generous helping of ex-lax placed inside a plastic cup, which I would've snuck inside the glass of soda she left on the table while she went out.
I ended up being too chickenshite to do it, partly because I didn't have the guts to poison her, but more so because I didn't want to make her extremely ill and have this shit blow up in my face (not literally).
One time I also thought about turning the toilet valve the other way during the day while she was all by herself, so she wouldn't be able to flush her crap (she's pretty dull so she wouldnt have figured out the reason why the toilet wouldn't flush, she'd have just assaulted the turd repeatedly with a plunger until she gave up and cried)