Those covers are REALLY tight from the factory. Why??? Maybe so DC can sell a few more parts after they get busted up. I don't tighten mine very tight and it always gives me grief when trying to remove it, don't over-tighten.
I've got about 180K between my 2 CTD's and I've only cleaned the inside of the canister once. There's almost never anything in there and if there is, the filter should catch it. I trust the filter more than my ability to completely clean something. Maybe once every 30k or so I'll drain a little FUEL out through the drain, but it's always just that, fuel, no water.