Using DD-WRT Router behind ISP supplied modem/router

[2975863j 3]

I have a fibre (xDSL) modem (192.168.1.254), supplied by my ISP which has only a few settings available through the GUI - can't even change the IP address!
Sitting behind this modem/router, and on a different subnet, is a DD-WRT router (192.168.0.1) which I use to connect to the AirVPN servers.
 
I am having a problem with DNS settings - there are so many on the DD-WRT router and a few on the modem/router, and I don't really understand how it works!
Just now the AirVPN website shows me as being connected, but a DNS leak test shows my ISP's DNS servers! For the last few weeks I have been getting around this problem by using the AirVPN client software to connect to the internet which works as it should.
 
Can anyone advise me on whether I just need to change some DNS settings to get it to work properly or do I need to add some admin commands in DD-WRT?

Maybe this would be worth putting in the tutorials section if it is resolved as more ISPs seem to be giving out routers with minimal settings?
 
Attached are screenshots of the DD-WRT Router [192.168.0.1] settings

If any more info is needed just let me know. Thanks in advance. :-)

[dj77 6]

Static dns3 add there a dns Server too example private ip 10.0.0.0 or Google dns 8.8.8.8 and Test on ipleak again

[zhang888 1066]

Alternatively you can use 0.0.0.0, in that case DD-WRT (technically dnsmasq but it doesn't matter) will ignore this resolver, and

you will have only one - 10.4.0.1.

[2975863j 3]

Thanks guys - both suggestions work! :-)