Muriatic acid is partially diluted hydrochloric acid. Used incorrectly and left too long in the plumbing, this highly corrosive acid will erode metal pipes and valves, leading to premature plumbing failure after repetitive use. Consequently, muriatic acid should only be used as a last resort when other methods fail to dislodge drain blockages. On the other hand, used with caution and applied correctly, muriatic acid will often help to dissolve clogged lumps of grease in your kitchen P-trap, and also dislodge balls of matted hair clogging shower and bathtub drains.
Ventilate the room by opening windows and turning on extractor fans wherever possible.
Pour 118ml. of muriatic acid into a glass measuring jug.
Position the lip of the jug directly over the drain outlet.
Pour the acid into the drain slowly and carefully without letting it splash.
Allow 10 minutes for the acid to dissolve the obstruction.
Open the cold water faucet enough to deliver a trickle of water into the sink. If the acid has worked and the drain outlet doesn't fill up, crack the faucet open another half a turn and let it run for two or three minutes. Once the water starts draining properly, open the faucet fully for another five minutes to flush all traces of acid out of the system.
Call a plumber to unclog the drain if the muriatic acid fails to clear the stoppage.
Rinse out the glass measuring jug with clean water immediately after using it to hold acid. Replace the childproof stopper in the acid container immediately and store the container in a well-ventilated area out of reach of small children. Wear a respirator, splash-proof eye protection and latex gloves when working with acid.