Sounds like you've hardly done any research on this method and are kinda just "shooting from your hip", which is a big no no. You can do it safely inside, as far as fire is concerned, but, as others have said, you might be endangering others with the CO. You should really do your homework. If intent on using the bathroom, you need to measure it (in meters) and calculate the volume of it - L x W x H. Then you take that number and multiply it by .135 kg/m³. That will give you the MINIMUM amount of charcoal to use. Multiply that by 4 for assurance. You need to light the charcoals (100% carbon, lump charcoal) outside and wait until they're glowing red and not smoking. THEN you bring them into the bathroom and wait for a while, maybe 20 minutes, maybe 30 minutes, to allow CO to build up. ONLY AFTER THAT do you enter the bathroom. You need to seal any windows thoroughly, around the baseboards, drains, etc. It's a very involved job. It's easier to do in a tent - smaller volume and easier to seal. You, also, need to place whatever metal buckets you put the charcoals in, on something that doesn't conduct heat well, like layers of bricks. You should put up a sign warning others of CO, so that they don't get asphyxiated when they find you. I don't like the idea of doing it indoors AT ALL.