Actually I used a pair of scissors to rough it up and yes it fits very tightly and works like a charm.
And as to how it is still white - well I guess I'll plug my dishwasher detergent here - I used to have that problem with Sunlight - once I switched to Palmolive, it comes out white. It actually removed the old stains.
I just broke a pair of scissors trying your method. Put the filter back in, added cold water for a test......................It worked!!!!! No leaks and no "filter float" !! can't wait to try with hot water in the am!! thanks...jim