Yes, they may have a patent on the filter but maybe not the way you use it. You could apply for a design patent but not a utility patent. I once invented a device that would hold a syringe needle so a nurse could recap avoiding contracting a disease etc. I spent several thousand dollars before I could get a medical company to pick up the idea and put into production. We had a patent attourney on retainer and even received our first royalty check. A few months went by and we were advised that the patent search turned up several similar devices and should drop the idea. About the same time the medical company decided to drop the device due to poor sales and offered us the molds and dies for several thousand dollars. I wasn't about to spend any more money and even lost the royalty check ($10.83). So my conclusion after jumping through all those creative hoops was, if you have a good idea for something either 1. forget about it or 2. put into production and hope someone doesn't sue you.

Planning my next escape...