just got finished going thru the "collection". found a brand new "mini". so 4ever's fliptop cap looks to be the easyest. (and litest). to live with. since this years hiking is on hold- I have a lot of time to think about the next outing. I'll make it a point of flushing after EVERY use.( once it's dead- I'll be moving on to a new filtering system.) one good thing, I was forced to get over my reluctance to drinking unfiltered water. if push come to shove, it's always there it to fall back on.... Thank you all for the help!