Emergency overflow chamber and algae

[Coralgurl]

Ive got 2 corner overflows on my tank, one is my main, the other emergency. Looking after maintenance items today and notice the emergency side is really gross with a sludge like goop around the drain, which was set up a few millimeters too low so it does drain a bit. I've also got hair algae in there. My thoughts are that there's no algae issues in the tank so is it harmful and should I clean it all out or leave it? I've got cheato in my sump and notice hair algae growing on the cheato as well.

I haven't tested anything. I'll be doing a water change later today so if required can make sure I have enough water to deal with the clean up of above.

What do others do with a dual drain system as far as maintenance is concerned? I've never drained that side to clean it.

Thanks