Unless you plan on using all the finish in the original container, you should pour the amount you expect to use into a separate container – for example, a clean jar or coffee can. It’s good to do this so you don’t introduce dust or other contaminants into the finish that you will use at some later date.
Especially with water-based finish, but a good idea with all finishes, you should strain the finish as you pour it. Convenient “paint” strainers like the one shown in the accompanying picture, are widely available from stores or online.
The reason straining is particularly wise with water-based finishes is that they are more likely than other finishes to contain solid particles of coagulated finish.