Your Android would need to be connected to an external firewall at all times through which you can monitor and control traffic. pfsense / firewalla are some of the popular firewall devices. Don't forget to remove the SIM card (airplane mode isn't enough). May need a wifi / cellular jammer too, to be absolutely sure the device will always connect via home router / firewall.

You could use an on-device firewall app, too; but OEMs / ODMs can always bypass it as they pretty much control not only the software but the hardware, as well.