Need some advice, the back drain hole on my 2002 Targa was blocked, water all through the rear, big job to dry it out, now I'm certain the blockage "material" is away from the drain hole for the moment but in time it will surely work it's way back down and may block the drain tube again, so I need to remove the curtqain (see photo) to give the chanel a good clean out -- but I cannot see how the curtain is attached.

Can anyone tell me how to go about removing the curtain?

Thanks