Basement below septic with no sump wont drain.

I own a property where a home burned down leaving a decent foundation we are turning into an open garden/patio area with no roof. The basement is below the septic tank and there is no sump, just a floor drain. The problem is that the open basement holds several inches of water for a day or two after rains. Tried to snake it but don’t get very far. There is a hillside where you would think it would drain to that also is swampy about where it should be but cant find a drain to open it up. Planning to dump some tracer dye down there but is there any tricks to clear old basement drains? Would it maybe just go to a bed of gravel or something? Do I have to dig it out or is there some type of boring tool I could rent to run a new drain?

 

If there was a home, was this floor drain for the basement? If yes there had to be a sump pump at one time but probably dump the water out onto the ground, not to the septic tank. Is there any power where you can dig a pit for a sump pump to add?