I get the same thing. I found your post because I was searching on ' waterpik has oder'. I'd describe the smell as an old sponge. I don't think rinsing with warm water is good, because bacteria like warmth. I use my waterpik at least 3 x a day, so I don't think how long it sits has much to do with it. The first 5 seconds of use smell, then not. I'm going to do what you're doing - letting the first 5 seconds go into the sink. Makes sense. Thanks for posting!