If it's any like the 404 I just obtained, once you have the filter set up with respect to your inputs and outputs and secured everything....just start pulling up and down on the primer....and don't do it gently....it wants you to take charge....then, when you have decided your arm may fall of if you have to push the primer any more....that lovely sound of water filling the canister can be heard.....and all is good in the land of Oz.