I smoke "bowls" or as we call them in Australia "cones" in my bathroom most nights, mums never caught me and knows what it smells like. i just leave the window a little open, have the exhaust fan on (having the window a little open makes it work harder, also makes more noise so you cant here the water) and having the shower on is not necisarry, but it help having the steam there to cover the smell abit, and try get as close to the exhaust fan as you can and blow the smoke towards it, and also once your done, wait in there abit till you know all the smokes gone, and also, if you are emptying the bong water in the sink, after you empty it, put some soap or something in it and give it a little clean to get rid of the smell bong water reaks! then when you leave, open the bathroom door up, and leave the exhaust fan on for a little while. This is how i do it anyway, my bathroom has now weed or smoke smell at all, and ive been doing for about a year now.