Instruct: Classify Amazon reviews into positive or negative sentiment
Query: fits medela pump, make sure to use the inner ring!

it does the job that i wanted it to do...which is to fit a medela pump and pump directly into an avent bottle. however, i noticed that milk leaks to the outside of the bottle while pumping. this has happened quite a few times, which is very disappointing. i finally figured out that you need to use the inner rubber ring with the converter. in retrospect, i missed something that was pretty obvious, but i wish there were some instructions that specified this.