The invention relates to drain cleaning compositions including relatively high concentrations of a hypochlorite oxidizing agent and a hydroxide (e.g., 4 to 12% and 2.5 to 10%, respectively. The composition further includes a surfactant (e.g., a surfactant blend, water, and exhibits a very high pH (e.g., at least 13). The composition is monophasic, even at high oxidizing and hydroxide concentrations. The surfactant may include a blend of an uncharged surfactant (e.g., an amphoteric surfactant or nonionic surfactant) and a charged surfactant (e.g., anionic, cationic, or a surfactant that becomes so under the high pH conditions of the composition). The ratio of charged to uncharged surfactant may be at least 1:10, e.g., from 1:10 to about 1:50.