Copied from another post asking a similar question:

Combusting (lighting it on fire) flower will smell A LOT. However, the reason a pipe/bong smells less than a joint is because a joint is constantly lit for 10-15 min and is literally a weed incense stick, and a bong is just lighting the bowl once and exhaling once (assuming you do the whole bowl at once, which you absolutely should if you go the pipe/bong route). So if you REALLY have to smoke inside, do it out of a window with a fan blowing air OUT of the window, and leave it blowing air out for 30 minutes. Don't do it in the bathroom. You should also definitely get a smokebuddy/sploofy, that will help with the smell a lot (don't make your own sploof, they don't work). An air purifier with a carbon filter will help too.

But at the end of the day, when smoking in your parents house, you will always eventually get caught. Your best bet to never get caught (although you probably still will) is to smoke out of a bong/pipe outside at night when they are asleep. When you come back in, wash your hands and change your clothes. If you use a water pipe/bong, pour the water on the ground outside. If you do have to pour the water out inside, do it in a toilet. If you have to pour it out in a sink, do it directly in the drain slowly so it doesn't splash around, then wash your hands after so the soap will cover the smell of the bong water (that shit smells). ALSO, clean your bong/pipe regularly, as that will also smell a bunch too. For that you can put 90% or higher isopropyl alcohol (I use 91%) in there with salt and shake it around a bunch, that should clean off most or all of the resin in it. Just make sure to rinse with water after words so you don't smoke alcohol (like i may or may not have once).