Sand in skimmer

[Andybme]

I have an in ground pool with a sand filter that I'm draining and I took out the skimmer baskets to clean. When I looked into the bottom of the deeper skimmer I can see two lines that must go to and from the filter. One of the pipes appears to be backed up or clogged with sand to the rim.

Does anyone know if I have a major problem or what might cause this?