went back to it over my lunch hour, filled it to the brim with water, emptied pail by pail, nothing. because there's nothing there. after looking underneath, which I hadn't before because it was dark when i started all this hoopla, i see the tank runs the width of the trailer ahead of the axles. the exit tube is on the end, so i suspect that because of its design, the tank naturally empties slower than our motorhome did. to further back myself up I took a flashlight and had a look, sure enough i see the far end of the tank and it appears to clean as whip. doesn't even smell bad anymore so i guess it drains slow and just needed a good rinsing for the aroma issue. thanks anyway, will keep that ice cube idea under my hat you never know.