Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Leaks!

Bought twin pack at Costco. Worked great the first time, then both mugs developed small leaks around the lids. The leaks not enough to soak me, but just enough to stain whatever I am wearing. Not a good thing on my way to work... I have tried washing and drying thoroughly between refills and tightening the lid, with no improvement. I am returning them to Costco today