Old pool construction question

First of all, great forum, I have found the answers to many of my questions in the past by reading through the postings. I have a question that I would like to post to the group on what may have been a construction method around 40 years ago. I recently moved into a house in Florida that was built in 1964. The pool is an in ground, concrete, 11,500 gallon oval shape structure. It was remodeled at some point, but was originally built at the same time as the house. I have included a picture of the deck opening and of a box built into the deck that seems to have the only pipe leading back to the pump. One of the neighbors told me that when these pools were built, the filter was located in front of the pump and this box is where the filter was located. Can anyone confirm that theory or know the purpose of this box? There is another connection capped off on the side of the box. Any idea where the capped off connection leads to? Main drain? I guess that I am curious if anyone has ever seen anything like this. I know that I haven’t and I don’t know of any of my neighbors with a similar setup. Thanks

My pool has something very similar to this. We think the pool was built in the late 60s or early 70s. We do have a main drain at the bottom of the pool that is plumbed separately<and leaking ;(>, but like you there is a fitting covering another pipe within the skimmer box. I don't know where it goes. We can't access our box from the deck though; we have to reach into the pool. I haven't been much of a help, but it is encouraging to find someone with a similar set up.

Thanks for the reply. I'll repost in the future when we remodel. I'm going to have to address finding out why the main drain isn't being used and adding more return lines. Only have one now. Also replacing that filter box with a new skimmer. Once the pool is drained we can start looking at the plumbing. I suspect that it still original under the pool. No idea what they used back then.. Iron pipe? The house plumbing is a combo or iron and copper pipe.

They used iron pipe and clay tile back then alot. Both of them are touchy, I have dug them up to find them imaculate, and also to find them to be garbage. It is a hit or miss thing, good luck.