Nu-Calgon - Gel Tabs are formulated with a breakthrough gel locking technology for treating air conditioning drain pans and lines. Keeps the drain pan from clogging and eliminates foul and musty odors. Four sizes are available: 3 ton, 5 ton, 15 ton, and 20 ton tabs. Multiple Gel Tabs can be added to the pan to acquire the necessary treatment for larger systems. Gel Tabs are easy to use. Put them into the drain pan and forget about them. When activated by condensation, the tablet will turn to gel and lock into place. This ensures that the tab will not move and potentially block the drain. Gel Tabs are designed to completely dissolve at an even rate over a 3 month period leaving nothing to remove when the product is done working.