I have a 30 yr old Concrete Pool
The skimmer box is just that, a concrete box in the wall with a weir (door)
in the bottom of the box, at the far side of the box, is a 1 1/2" drain hole (Pipe runs to filter).
The bottom of the box - approx 5"x8", is covered with a removeable metal plate with ~1/4" holes to catch leaves.
(PS. Does anyone know where I can find a replacement for this grate? It is broken in 2 and badly corroded).
There is an Identically sized box right next to the skimmer, this box does not have any drain in the bottom.
Instead it has a 1/2" pipe leading into it near the water level. It does not open into the pool . The pipe seems to come from the return as is fills the box with water through this pipe, there is another hole between this box and the skimmer which allows the overflow from this box to pour into the skimmer. The pipe terminates with an elbow that points down into the box. the elbow is not threaded.
My guess is that this is some system to prevent the skimmer from running dry if the level of the pool drops. But if this is the case it does a pretty poor job, since anytime my level drops that low, this pipe cannot fill the skimmer fast enough to prevent the pump from sucking air. Anyone know what this is?