A suggestion:

Flush the empty packaging with water at least three times and return the liquid to the pesticide storage tank. Use the residue during (pesticide) application.

More context would be helpful, but I believe that the point is that the residue that remains after the rinsing of the empty pesticide packaging is efficient enough to also be used during application of the pesticide to the crop.

Pesticide application - from Wikipedia
"Pesticide application refers to the practical way in which pesticides, (including herbicides, fungicides, insecticides, or nematode control agents) are delivered to their biological targets (e.g. pest organism, crop or other plant). Public concern about the use of pesticides has highlighted the need to make this process as efficient as possible, in order to minimise their release into the environment and human exposure (including operators, bystanders and consumers of produce)"

--------------------------------------------------
Note added at 43 mins (2017-05-09 10:33:51 GMT)
--------------------------------------------------

Also check out this link:

http://www.syngenta-us.com/env_stewardship/futuretopics/inde...

"2. Rinsate


Rinsate is pesticide-containing water (or other liquid) that results from rinsing a pesticide container, pesticide equipment, or other pesticide-containing materials. Rinsate is much more diluted than excess spray mixture and can be used as part (up to 5%) of the water (or other liquid) portion of the next spray mixture of that chemical, if used the same day."
..."Collect rinsates, filter out any debris, and use as part of the make-up water in the spray tank for the next application of that same pesticide product."

Hope this helps!