One skimmer drain, no main drain and sand filter.. skimmer not sucking in water

[PureLuck]

I was trying to help a friend open their pool this afternoon and ran into an issue. The pool has only one intake, a skimmer no main drain. They also have a sand filter. I'll attach pictures. We removed all the plugs, opened the valves and turned the filter on. Nothing. The pump is working fine, the return (only one of those as well) is working as I filled the pump basket with water to see if priming it would start the suction.
Tried using a plunger as well, and nothing. The water is not making it's way through the pipes to the filter. Any ideas??

 

[Texas Splash]

I wonder if that ball valve failed? What does the line next to it (currently closed) go to?

 

[PureLuck]

No idea. They just bought the house last year. I thought it strange that there were two pipes coming from the pool when only one drain.
I did try opening and closing them in different intervals to see if it would open things up.
They have a sprinkler system, there's no chance that the pool is connected to that, right?

 

[Texas Splash]

They have a sprinkler system, there's no chance that the pool is connected to that, right?

Shouldn't be. I mean those two pipes are both going to the pump intake, so we know they are suction. So based on what I'm hearing, I can only assume one of the following:
- The left pipe is either clogged, broken, or has defective ball valve
- The right pipe? The mystery pipe. Do they have a suction cleaner at the pool maybe?
- You keep saying drain, but then also skimmer. Do they have both a poolside skimmer and a lower main drain?
- Is the O-ring under the pump's clear lid in place, clean, and lubed with pool silicone? Same for pump drain plug?

 

[PureLuck]

Shouldn't be. I mean those two pipes are both going to the pump intake, so we know they are suction. So based on what I'm hearing, I can only assume one of the following:
- The left pipe is either clogged, broken, or has defective ball valve
- The right pipe? The mystery pipe. Do they have a suction cleaner at the pool maybe?
- You keep saying drain, but then also skimmer. Do they have both a poolside skimmer and a lower main drain?
- Is the O-ring under the pump's clear lid in place, clean, and lubed with pool silicone? Same for pump drain plug?

Did not see any suction cleaner, or a lower main drain. Only a skimmer.
The suction seems fine, it could use a little lube. Both pipes were in the off position when I arrived to help them. I tried different configurations, but no idea what that second pipe is.
I will ask them about the liner, I wonder if the previous owner replaced the liner, but didn't cut out the deep end main drain? They only had the pool so far one season.

 

[IceShadow]

Is there a weir door on the skimmer? Edit: never mind, no water pull at all, ignore me.