You can poke the spout (with a toothpick or something that's not too hard), or, if you are less genteel, you can blow into the spout (between infusions). It may be easier to first pull the leaves inside the pot a bit away from the opening, and then gently clean out the spout.
You can also make it less likely to be clogged by building the tea carefully (especially if there are a lot of broken bits), and then pouring in a fairly controlled way.
Sometimes the problem can actually be with the airhole on top, so make sure this isn't blocked or too small.
There are also some metal filters which you can put in the pot. Some people don't like them; I personally don't go out of my way to add them to single hole pots, but usually I don't take them out either, and I haven't found any issues with a metallic taste.