If it were me I would put it in a Rubbermaid trash can and stir/ rinse it with change water from your DT. Sounds like some of it is beyond anaerobic and borderline anoxic (hydrogen sulfide) the black stinks like rotted eggs. You could also have a ton of trapped NO3 in it and detritus . If stirring and rising with change water isn't getting the job done and you still show a lot of NO3. Then rinse it with a garden hose as a last resort and do one last RO saltwater rinse.