sponges growing in overflow... how to get rid of them?

[LostMind]

I have a cpr 1600 or somesuch overflow (it kinda sucks, but better nothing), which has been working for several months with no real problems (except loss of suction once in a while)...

but now I have a new problem... the inside of the damned thing has some sponges growing in it and, they are growing large enough that the amount of water flowing thru is slowing down.

I am guessin I have to take the overflow off the tank and soak it in vinegar or something to get rid of these buggers? anyone have any suggestions on how to clean it otherwise?

Thanks!