Where do these two pipes go?

[Justice Distributor]

Please focus on the return-side plumbing that follows the left valve actuator.

Pipes from left to right:

2" - spa jets

2" - paramount six-port water valves (two) (both get pressure even when all the return side valves after the actuator valve are closed)

1" - ? (open and close 0.5 PSI bounce 0.5 PSI change)

1.5" - ? (open and close 4 PSI bounce 0.5 PSI change)

2" - spa spillway

There's an IDC (in-deck debris canister) but it's non-venturi (not return-side powered).

There are wall returns but they are plumbed to one or both of the paramount six-port water valves (they intermittently have flow).

 

[JasonLion]

There is no easy way to figure it out, other than turning them on/off and seeing what changes with the pool.

One possibility is a spa overflow line, that runs a little water to the spa even when it is otherwise turned off to keep the spa overflow waterfall going. Another possibility is a waste line that runs to a drain or dry well.

 

[Bama Rambler]

Can you lighten up that pic a little? It's hard to tell how everything is connceted.

While it's impossible for us to actually know (my ground penetrating radar won't work through the internet :-D ) That 1" is probably a bypass to keep some flow to a water feature (i.e. spa spillway) or a bypass around the popups.

Is the 1½" you're asking about the one with 'in deck debris canister' written above it?

 

[Justice Distributor]

I found out what they do.

Pipes from left to right:

2" - spa jets

2" - paramount six-port water valves (two)

1" - in-deck chlorinator (I didn't notice the water moving in it because there was a cap over the hole)

1.5" - non-water-valve floor nozzles

2" - spa spillway