Instruct: Classify a given Amazon review into positive or negative sentiment.
Query: Buy Duck Bill Valves! Not bad, for once or twice pumping per day

It is a very cost-effective manual pump if you only need to pump no more than three times per day.The only problem I had with this one is that you need to replace the star valve every two months(given you're occational pumper). When the valves ran out(there're 4 coming with the order), I called the customer service to purchase more. The rep told me that there were another valves available that are called "Duck bill valves". So I ordered 6 for $6.00 at Amazon.I have used the Duck Bill valve for three months, and it is still working pretty well. So I strongly suggest that you should have Duck Bill Valves stored if you purchase this mantual pump.