Hotpoint Dish Washer Not Draining

It looks like mold or black mildew.

It commonly starts growing on and in the door gasket, which is somewhat porous. It collects on the filters until, as you have learned, you clean them. Then small pieces escape and stick everywhere.

Bob Villa and others recommend bleach or vinegar for controlling mold in a dishwasher. But your infestation looks too far advanced for such mild treatment.

You should use a cleaner called Affresh which was designed by front load washer manufacturers to remove mold and mildew build up.

Unfortunately Affresh and like products are not good at cleaning the mold from porous rubber parts. Try flexing the gasket away from the tub and scrubbing behind it with a stiff toothbrush.

If this doesn't work then you will probably have to replace the door gasket. The part costs around $80.

You want to make the run as high as possible early on and here's why.

If you mount it low, then the water comes off the pump with a lot of energy, runs along (losing energy) and then has to climb a hill. This means that you have a potential backwash situation and you have a LOT of water sitting in the drain line. I found this comment from Bosch to be helpful

The high loop in the drain hose of your dishwasher is to keep water from settling in the hose if it were hanging down any lower or horizontally. This keeps the drain hose dried out and keeps any odors from backing up into the dishwasher.

So I would run the drain line high and then slope it down so can drain and stay empty and dry. The less water you have standing in the line, the better.