Does my hole coring suggestion sound a good option.

I think I’m going to get some core holes drilled into the sand base and from the side like my patio concreter has suggested. Then use a flexible pipe ...

Thanks for that. It’s an option.

Thanks but it’s metal. And we get snakes so hence the small gap so we don’t get visitors.

The photos are the low points where the water gathers when flushed out and washed with a hose.

There is roof as it’s fully enclosed. There is little or no water from the roof. Because we have dogs in the patio the issue is flushing the patio out ...

Photos attached. Possibility is to core a pipe through the concrete at an angle through the outside retaining wall, or cot a channel. Don’t know which ...