If I had an oriental rug that I wanted to dye dark gray, I would take and lay it out on the lawn on a tarp. (Or maybe stick it in the tub, if it fit??) I would take a strong solution of dye and saturate the rug. Then I would scrub at it with a broom or something, and keep adding dye, and do this for half an hour or whatever the box says to process it for. Then I would hose it off, and do a rinse with vinegar-water or salt water, or whatever you are using to set the dye. Then I would hose it off again, and hang it over the line to dry. That is only my best guess as to what I would do, as a suggestion.