Login or register (free and only takes a few minutes) to participate in this question.
You will also have access to many other tools and opportunities designed for those who have language-related jobs (or are passionate about them). Participation is free and the site has a strict confidentiality policy.
Explanation: A sprayer reservoir could be anything, but I believe it usually means a part of a sprayer used in gardening.
In a Web site, I found the following explanation:
Home gardeners have an adequate selection of pesticides labeled for home use,--(snip)---Probably the two most popular applicators are dusters and hose-end sprayers. --(snip)--These types have a reservoir that is filled with the dust. --(snip)--Pesticide concentrate is placed in the reservoir of the hose-end sprayer and water added based on the volume of spray needed. --(snip)--The hose-end sprayer reservoir must be rinsed after each use.
There are quite a few Japanese Web sites that show sprayers - please have a look at the site below to confirm a reservoir of a sprayer is called "Tanku" in Japanese.