supposidly puting a few drops of bleach in ur piss makes a sampel come out negative but this throws off ph and other things which could indicate the test was tampered with. If your parents give u a random home test ur best option is probalby to chug as much water as possible and ur piss will either come up negative or no result and if it comes up no result then that could maybe buy u enough time to consider other options. If your really concerned tho i think maybe you should just get an emergency stash of clean piss and keep it hidden somewhere.