/usr/lib/unifi/data/sites/default/config.gateway.json:

{
	"service": {
		"nat": {
			"rule": {
				"1": {
					"description": "Redirect DNS requests",
					"destination": {
						"port": "53"
					},
					"inbound-interface": "eth1",
					"inside-address": {
						"address": "192.168.0.105",
						"port": "53"
					},
					"source": {
						"address": "!192.168.0.105"
					},
					"log": "disable",
					"protocol": "tcp_udp",
					"type": "destination"
				},
				"6000": {
					"description": "MASQ DNS requests to LAN",
					"destination": {
						"address": "192.168.0.105",
						"port": "53"
					},
					"log": "disable",
					"outbound-interface": "eth1",
					"protocol": "tcp_udp",
					"type": "masquerade"
				}
			}
		}
	}
}