Hooking up a garden hose to a container of weed killer is merely a matter of attaching the container to the hose nozzle. Most weed killer products come either with an attachment for connecting to the hose or as a package manufactured with a built-in nozzle, such as Roundup weed killer. Once connected, the pressure of the water flows through the weed killer container to spray the chemicals.
Turn off the water to the garden hose at the outdoor valve by twisting the knob clockwise, and then remove any nozzle attachments, such as a sprayer, from the end of the hose.
Pull on a pair of rubber gloves. Some weed killers can cause skin irritation.
Attach the end of the garden hose to the weed killer container by threading the nozzle onto the weed killer valve and screwing the hose coupler counterclockwise. Hand-tighten the connection to prevent weed killer from spraying through the edges of the nozzle.
Turn on the water at the outdoor value and pull the trigger on the container of weed killer to spray the product on the lawn according to the manufacturer's instructions.
Shut off the water to the garden hose, and then disconnect and discard the weed killer container when finished.
Flush the garden hose with water before spraying garden plants and flowers in case any chemicals have backed up into the hose while you disconnected the product.