Cleaning skimmer collection cup?

[Son Of Skyline]

How do you guys clean out your skimmer collection cups? I've been periodically flushing it with clean water but I've been leaving alot of the scum that sticks to the sides. I can't seem to reach in there enough to clean the sides out. Is it ok to just leave it and just keep flushing? Sorry for the newbie question...I'm still new to this skimming thing (I've been skimmerless up until recently). Thanks in advance...