Smoking in the bathroom is my preferred method. I blow smoke through a dryer sheet tube (paper towels tube, not toilet paper... it's twice as long) and into a vent, and hold my pipe or joint right under the vent.

Here's the key to good airflow... EITHER unseal the door or open the window. If the window is furthest form the vent, open it. Otherwise, use the door. This gets the air flowing across the room, taking all that smokiness up into the vent with it.

But the best way I've found is to just heat up a knife with a lighter and press it on a bit of bud, inhaling the resultant vapors. The strongest smell after doing this is you breath, you don't need to use a tube or anything to mask the scent. You go through lighters pretty fast, but it's definitely worth it. Unless you have shitty weed on need to smoke a lot... I usually only need at most a quarter of a gram.