I changed the DNS settings on my phone (Oneplus one) to cloud flare and then to OpenNic.
On https://ipleak.net/ the phone shows the new DNS servers, but when tethered to my laptop via wifi or USB the default operator DNS is still being used.
I reset the connection on the laptop but it still connects to the operator.
I tried entering the DNS settings directly on the laptop but nothing would load (but this is probably the laptops fault (Linux Mint 19.1) not /e/ )
It seems the OS is ignoring the set new DNS option when tethering.