What tools to resolve UDM's WAN DNS queries?

[EntropySmoke]

I have my own local DNS server on a separate (Raspberry Pi). I use it to resolve DNS queries for all local clients, but I run into a problem when I try to use my local DNS server for UDM WAN DNS. UDM makes its own connections to Ubiquiti servers for all kinds of reasons. I need to monitor and filter those requests, but if I specify LAN DNS server IP for WAN DNS server IP, I immediately get a ton of ACK scans from WAN and from ISP. My ISP doesn't like when customers run their own DNS servers. On their own equipment (which I do not use), they allow changing LAN DNS, but not WAN DNS.

UDM WAN port is eth4 interface. If I use my local DNS server's private IP for WAN DNS, then all WAN DNS requests are routed from eth4 to local DNS server IP. I need to force UDM to not use eth4 for DNS resolution. I have to make UDM's WAN queries use local DNS server, but not have those queries routed from eth4. I need UDM DNS queries to be made directly from UDM localhost to local DNS server IP and not go through eth4 interface. I don't know how to do that. I try to improvise and adjust /etc/resolv.conf and /etc/dnsmasq.conf files but UDM WAN DNS queries still use eth4 interface before reaching local DNS server address...

I know I can use custom IPTables, but I am not proficient. INPUT and OUTPUT rules are used by UDM itself. Clients use the FORWARD rules. If I create rules that fully block eth4 interface for INPUT and OUTPUT, then it has no negative effect on clients, but prevent UDM from making any DNS queries and from receiving updates. I hope I making sense...