Thanks for all your reply, i dont have a blocked drain, but just have occasional problem with sewer smell comming out of the drain from the bathroom. i initially thought that since caustic soda is a strong base and the heat from the reaction with aluminium would sterilise the drain solving the problem, but then i read the label on the container and said that i should not put solid caustic soda directly into the drain... but yet again, i saw product like draino which have similar composition (ie, NaOH and Al) which direct us to directly apply it to drain... :confuse: anyways, i know i'm rambling and probally not stating my problem clear, but does anyone have a solution to my problem? (ie the sewer smell)...