The traditional way to make Thai iced tea is indeed to strain it back and forth through a cloth filter, making the tea stronger each time.

You can buy a small cloth filter at Asian markets (and some Latin American ones, too, where it's used for coffee). The filter looks like a small muslin cone with a metal ring at the top and a handle sticking out. That's easier to use than cheesecloth. I'd still recommend pouring the tea back through the filter a couple of times.

Susan