Let’s take a closer look at these factors…. The pros of using a combi boiler are. Depending on current work load and availability. Caustic soda has an exothermic reaction when combined with water, meaning it heats and produces a “fizz”– which might just clear your blockage. Drain cleaner with natural enzymes great for slow drains safer products for your kids, pets & family removes build-up & helps stop clogs before they start keeps drains & garbage disposals smelling clean.