Grazon is designed as a spot treatment to spray off small patches of weeds in a field. The ideal is that you go round with a knapsack sprayer just treating the weed patches.
Also if you want it to work, you need to spray the weeds at the right stage of growth - when they are growing quickly but not big. Generally called "rosette" stage. If they are smaller they won't absorb enough spray through the leaves and bigger than this, and the plants will be too strong to be affected much. I would think that you are probably too late in the growing season now. Having said that you could try cutting the weeds and then spraying as they regrow.
Given that it is a spot treatment there will be areas of the field that you haven't sprayed that you can collect the muck from.
If you need to do more that spot treat, you need to use a different spray.