These are available from most supermarkets and convenience shops and can be a liquid or solid corrosive. They’re normally filled with sodium hypochlorite, sodium hydroxide or potassium hydroxide, with up to a 50% concentration.
These chemical drain cleaners are very easy to use, and by following the instructions, they’re normally poured straight into the sink or drain. The cleaner then reacts with and disintegrates the blockage.
While the advantage is they’re readily accessible, chemical cleaners are known to lack effectiveness on blockages far away from the drain opening.
You also have to maintain extra caution when using, as they could damage skin, clothes and eyes if used incorrectly.