A swimming pool inline leaf canister is designed to trap leaves and other large debris before they enter your pool's filter system. They are used inline, that is attached in the middle of two lengths of hose in between your automatic pool cleaner and the skimmer box.

The benefit of a leaf canister is it is three times larger than your filtration box. If you are constantly emptying your filter box due to trees dropping leaves, the leaf canister will trap a large amount of leaves. You wont have to clean the filter box out as often and as the leaf canister is clear, you can easily see when it needs emptying.
   

Features

Choice of mesh bag or basket: focus on smaller particles or big leaves before they reach your pump
No Clog Design: ensures constant water flow to pump
Easy-Open Lid: for quick access
See-Through Canister: lets you see when to clean
Can be cleaned while still in the pool without disconnecting the hoses

Contents of box

Leaf canister
Basket (use the basket or the mesh net)
Mesh Net
Hose - Type B Adaptors, Flexi Adaptor, Male - Male Leader
Continuous Hose Joiner

Installing the Leaf Canister to your pool cleaner is easy 

Turn off pump
Refer to hose application guide for correct adaptors
Disconnect the first and second section of the pool cleaner hose from the skimmer box or suction fitting and using the correct adaptor (if required) connect to body of the Leaf Canister
Attached male-male leader to lid (if required) then connect remaining male-female pool cleaner hose to the Dragonfly Floating Pool Cleaner
If hose is continuous, cut the hose 1.0, to 1.5m from the skimmer box and use hose joiner to connect to lid of the leaf canister.
Ensure to purge all air from and leaf canister before use. To open canister depress latch on handle and turn in "open" direction to open lid. Submerge Leaf Canister until filled with water. With Leaf Canister still under water, turn lid in "close" direction and close until you hear it click into place
Check all hoses are connected to skimmer/suction fitting and pool cleaner before turning pump back on.

For more information, this article may interest you "Leaf Canisters - the underrated pool accessory"