Alkaline drain openers primarily contain sodium hydroxide and some may contain potassium hydroxide. They may appear in liquid or solid form.
Liquid formulations of corrosive alkaline drain cleaners can contain sodium hypochlorite NaOCl (bleach), sodium hydroxide (lye), or potassium hydroxide (caustic potash) in concentrations up to 50 percent. Other corrosive mixtures come as two-part cleaners that are mixed as they are poured in the drain opening. Inside the drain the two solutions react to release a gas, and surfactants trap the gas as dense foam. The intent of this foaming action is to coat the inside of the drain pipe to dislodge more of the substances that form the clog.
Solid formulations of corrosive alkaline drain cleaners in the form of sodium hydroxide or potassium hydroxide granules can provide more concentrated effective ingredients. Some patented, solid-formula cleaners add aluminum turnings that react with the solid hydroxide in water to heat the caustic mixture to a boil.
Alkaline drain openers can dissolve hair (containing proteins) and fats inside pipes via alkaline hydrolysis of amide and ester respectively:
RCONH2(amide or proteins)+ OH- ? NH3 + RCOO-
RCO2R’(ester or fats)+ OH- ? R’OH + RCOO-