Clean the spa’s plumbing before draining it. Drain Prep is designed to effectively clean spa plumbing by removing the accumulation of organic matter! Contaminants build up in the circulation system and the pump. Emptying the spa without product, without DRAIN PREP will not remove organic waste (skin-cream-soap etc.). Emptying the spa using the pipe cleaner minimum 2x per year is highly recommended. The drain prep is distinguished by the presence of enzyme inside the product allowing a deep cleaning. It is important to put the product in the spa water before draining it. The instructions will tell you in detail the steps to follow, but you must remove the cartridge before using the product.