Cascading proxy server on 3peoxy, How to set it up?

Question

ubuntu

Everywhere on the Internet there are articles about how to set up your proxy on a given package and everywhere just outgoing traffic goes through the port.
How to configure this way

Input proxy server Outgoing proxy server
1.1.1.1:8000 -> 12.12.12.12:1234
1.1.1.1:8001 -> 20.20.20.20:5678
1.1.1.1:8002 -> 50.50.50.50:8899
And so on for a hundred ports and proxies.
Still, the exit addresses would be grabbed from the file with some kind of periodicity.

Answer 1

Accurate to proxy types

allow *
parent 1000 http 12.12.12.12 1234
proxy -i1.1.1.1 -p8000
flush
allow *
parent 1000 http 20.20.20.20 5678
proxy -i1.1.1.1 -p8001
flush
allow *
parent 1000 http 50.50.50.50 8899
proxy -i1.1.1.1 -p8002
flush