When I was living with my parents and needed to hide diapers I would place the diapers in my closest behind some clothes.
You could also hide the diapers in an old computer case, under your bed, under your mattress, in the attic, in a locked box, behind your dresser or even in a filing cabinet.
To get diapers without your parents knowing you can order diapers online and have them shipped to your door discretely which most diapers are shipped discretely.
Or take a backpack with you to the store and then put the diapers in the backpack and then bring them in the house that way.
Or buy the diapers, place them somewhere outside in your backyard and then retrieve the diapers once you're inside the house by going out your bedroom window etc.
If you can do so you can have UPS hold the diapers for pick up or use an Amazon Locker.
When I lived with my parents and bought diapers I would take my backpack with me to the store.
Then I would go into the store, buy the diapers and then after I got out of the store I would put the pack of diapers in my backpack.
Then I would bring the diapers into the house with my backpack.
I also sometimes used to get the diapers, take them around behind my house, sit them near a window and then go inside, open my bedroom window, crawl out and get the diapers and bring them inside that way.
Another option now is if you can order diapers online and have the diapers shipped to your door discretely and then get the package before your parents see it.
When I lived with my parents and needed to dispose of diapers I would place the diapers in small grocery bags and then when my parents were asleep I would sneak the diapers out of the house and into the outside garbage can.
I usually waited until the night before garbage day when the garbage truck would come around the next day so the diapers would not still be in the trash can.
I would hide the dirty or wet diapers in my closet behind some clothes so they could not be seen and mostly my parents never came into my closet as I had to put my own clothes away.
But I would just hide the diapers in the closet and then wait until the night before trash day and sneak them into the garbage.
However another thing I used to do as well was to take the diaper into the bathroom and then rip the diaper open and dump the SAP into the toilet.
Then I would flush the toilet and then cut up the rest of the diaper into small pieces and flush them down the toilet a few times as well.
If you have your own trash can in your room then you could bury the diapers in the trash bag and then take your trash out yourself and then your parents would likely never notice you have diapers in the trash can.
Or take the diapers outside and bury them somewhere in your yard or put them in your backpack on your way to school or somewhere and then throw them in a park trash can or other public trash can.