Ewwwwww..
I think I'd pull the drain plug first and probe around with a screwdriver in there.
If it's mud-like sludge, pull the pan & clean it out. Put the pan back on.
Oh, and a filter too!
If you can get the oil down a couple quarts, I'd try adding a couple quarts of tranny fluid and see if you can gently thin out and then flush the old oil.
Good luck!