There is a wide range of glue's, but a lot of guys seem to use Platic weld. Tenax used to be a popular brand in the US, but i believe thats no longer around. I assume you are in the USA, i can't recall what the most popular brand is over there.
You can use a fine old paintbrush to apply it along the joins. There is also an item called a Touch-N-Flow. I have only just bought one and not used it yet, but it gets lots of praise.