Without getting into replacing the entire system with a modern septic tank I would offer the following.
It is very possible to install a leech system here but will take a little extra work.
In Thailand, I have successfully installed both septic system leech fields and French drains for run-off water.
1. Research leech system design online and in English
2. Research Gray Water recycling in the USA. If done properly, many systems are now fully approved.
Use a combination of the above research and local conditions to design a safe, and effective system.
3. Perforated pipe is generally not available in Thailand…I make my own by using an angle grinder to cut slots in the solid pipe.
This is faster and easier than using a drill.
4. Drainage gravel should be 3/4” or larger with no fines. It should also have a layer of geo-textile cloth surrounding the gravel and pipe to prevent soil intrusion which reduces the air in the drainage system and thus reduces drainage and the aerobic bacterial action required to treat the leech water.
5. A leech field can be located far away from the septic tank as long as the water can freely move within the pipe.
There is more, but do some research and reply back after you get a basic design.