Inground oversized hot tub - plumbing/main drains

[Mrgreenhimself]

Hi everyone,

I have an oversized "spool" which was unfortunately left in a horrible state by the previous house owner.
Planning to have it re-plastered etc.

However, my question is related to the many, many drains, jet holes, and other holes I see.
At the bottom I have 2 main drains. They are connected to the skimmer which has 2 holes. The hole going to the pump has great suction, but there is very little suction at the bottom main drains - even if I starve the skimmer to direct the suction via the equalizer line to the bottom main drains.
I snaked the lines, and there seem to be no blockage. Anyway - that is also for another day.

My question is about the round hole at the top of the pool, and the 2 other "main drain" looking holes. They have same grate covering them as the bottom main drains.
Can anyone advise what those 3 holes/drains are for?

Attached is a picture.

Thanks a lot!

 

[1poolman1]

Hole at top, likely fill (perhaps overflow?). Four "main drain" ports - enough for 2 pumps. Filter pump and jet pump?

 

[Mrgreenhimself]

Hole at top, likely fill (perhaps overflow?). Four "main drain" ports - enough for 2 pumps. Filter pump and jet pump?

Ahhh of course! Haha rookie mistake!
Yes, the 2 drains on the wall are most likely for the pump operating the jets. I was so focused on the bottom main drains and the lack of suction, that I never even thought of the other pump.
I am thinking that hole at the top is an overflow drain, but I am not sure where it goes. I'll have to snake that later.

Thanks!