clean it whenever you want and/or get bored. you can use rubbing alcohol and salt, both are pretty cheap. get rock salt or epsom salt, they have bigger crystals. depending on the size of your bong, use 1/2 bottle or so. and maybe a 1/3 cup of salt. and just swish it around. if you do this often (once a week or so) it should stay pretty clean.

your room won't smell like bong water unless you spill it, then you wanna clean that shit up quick as bong water is nasty. i try and change my water few smoke sessions, but sometimes you get high, forget and it'll stay in there for a few days, but its not a big issue.

enjoy your piece.