I would dump (recycle) the black hose and buy a new one.
Clean your Platypus or any other water bottle right after your trips. Platypus sells a cleaning kit with long brushes for both the bottle and hose. One thing I also do is drop a tablet of denture cleaner into the bottle and let it soak for 15 minutes - thankfully, this is the only reason why I have ever purchased denture cleaner. Then, if you are going to store it for a while, use a $10 aquarium pump with some hose to dry it out. I bought some "T" connectors so I could dry out a couple of bottles at the same time.
Sometimes, if I know I am going to use the bottles again pretty soon, I just refill them with water and put them in the fridge.