Abstract: A conversion kit for converting an existing sprinkler system liquid supply line into a general purpose soluble chemical application device is used to apply insecticides or fertilizer. The easily installed kit mixes dry chemicals with an existing pressurized liquid to form and expel appropriate treatment solution. Spent dry chemicals can be easily replaced in a removable canister. Chemicals from conventional bulk packages or specially prepared packets may be used. A safety interlock shutoff valve is provided to prevent pressurization of the system while chemicals are being replaced. A vacuum breaking air vent valve is provided to allow drainage of liquid from the system. All components are enclosed within and supported by a single housing. The housing is preferably molded from a durable plastic material.