Thanks for the responses.
What exactly is a suction side cleaner? Is this a dedicated line for a vacuum or something?
The reason I'm asking about the lines is that I attempted to vacuum today for the first time so I had to experiment with the valves to get enough suction to keep the vacuum hose on the skimmer port. It would only stay put with one skimmer (#1) and the main drain (#3) closed, but the vacuum still wasn't moving much on the bottom. I'm wondering if closing #4 will help. Also, when I closed #1 and #3, the pump pressure eventually rose about 5 psi. I didn't know if this was due to the vacuum doing its job or the pump working extra hard with only one line open.