someone just passed this on to me:

Pour 1 gallon of white vinegar into a bucket. Everyday 5-percent household white vinegar is fine for this weed killer. You won’t need higher, more expensive concentrations such as 10 or 20 percent. It may take two or three days longer to kill the weeds with the lower concentration, but they will die.
Add 1 cup of table salt. Stir the solution with a long-handled spoon until all the salt dissolves completely.
Stir in 1 tablespoon of liquid dishwashing soap. This will act as a surfactant and make the vinegar and salt solution adhere to the weeds more efficiently. Blend thoroughly.
Funnel the weed killer into a plastic spray bottle.
Drench the weeds with the solution on a dry, sunny day. Coat all surfaces well with the spray. Any plants soaked with this solution will die within several days. They won’t be back and nothing else will ever grow there.
Funnel any leftover weed killer into an empty plastic container. Cap it tightly. Label it clearly and store in a cool, dark spot indefinitely.

Things You Will Need:

• Household white vinegar
• Bucket
• Table salt
• Long-handled spoon
• Liquid dishwashing soap
• Funnel
• Plastic spray bottle
• Empty plastic container