Low suction in skimmer

[Speedy]

3 Things: I bought a house with an inground pool and am trying to open it.
1. The pool has a skimmer on either end. One works fine, the other doesn't flow enough to even submerge the plastic filter basket. Could the line be plugged and if so, how would I clean it?
2. Their are two "holes" at the bottom of each skimmer, one contained the plug from the winter that I removed. The other looks like a small catch basin that is only a few inches deep although I'm not sure if this is what it is?
3. After initially running the pump, adjusting chemicals and running again, what is the best way to clean the main filter in the pump?
Thanks to all for all your help.

[Pool Helper]

To answer your pool opening questions:
1) If there is no apparent plug and some suction at the skimmer, plug the first skimmer in the hope that the pressure will open the second skimmer;
2) The second indentation is part of the skimmer design and in the models I use has no real funtion;
3) You probably have a multiport valve. To clean the filter (sand filter) turn off the pump and move the valve to backwash (directly opposite the filtration position). Turn on the pump. When the water flows clear through the observation window turn off the pump and move the valve to rinse (10 o'clock position). Run the pump for 20-40 seconds. Finally turn back to filtration and you're done.