Yes, psuedomonas is a "water bug" so it is usually lurking around sinks, showers etc. So trapping and leaving standing water in the neb cup could start psuedomonas growing, then you dump in your meds and inhale away!
Long ago I called our nurse and said "gee, it gets late at night, we wash the cup and don't want to wait for it to "air dry" can we use a blow dryer to get it dry before we use it. To which she said, well using it right away would probably be fine, but why don't you have more than two neb cups?..... This has been discussed with several other moms, who never really knew it was possible to get more -- we found out we the insurance company will purchase 4 new cups per year. They are to be used for one year and then thrown away, we figured without the everyday use, we should be able to use them for at least two years, so we rotate in and out but are always able to keep 8 cups in use, this way we only have to wash and sterilize cups once a week.