Send the make-up batch from the mixer to the agitator

While this is being done the control valve on the standpipe should be turned off in order to get effective blending. However this turning off should be as brief as possible so as to not lose the hole.

When all the make-up batch has reached the agitator, take a measurement of the total volume of grout in it. Then open the control valve and carry on with the grouting.