We have used a mixture of dish soap, white vinegar, and salt. This will kill the grass too, so use it carefully.
Regular household white vinegar is fine.
Good old plain white vinegar. I have 5 gallons in my closet right now, hundreds of uses for vinegar!
Buy vinegar with acid 3.5 to 4%, it's on the label.
I would use the least expensive, like white distilled
Regular white vinegar works well - but you can buy a stronger version of it in some stores (it should be labeled that it isn't used for food purposes).
White Vinegar... I am betting that unwanted pickle juice would work too
Don't use the salt, it causes problems with drinking water, streams rivers and lakes, causing the salinity level to change. Many fresh water lakes and streams are seeing higher salinity levels already, even some cities are seeing higher salinity levels in their drinking water. Plain old vinegar works if used judiciously to not kill off wanted grass and plants. The soap will help it adhere to the leaves.