Darkoshi

I use my water pik about 2-3 times per day. I have noticed a very distinct odor which smells like almost a fungus or even mold. I try to keep it very clean. After using I take the whole base unit turn it upside down, hold it high and drain out the water that is left in the hose between the base unit and the mouth piece. Still has the odor and would sure like to know how to get rid of it.