/ip address
Link(1) - 192.168.1.2/24 = WAN1
Link(2) - 192.168.2.2/24 = WAN2
WAN-OUT = 192.168.10.2/24 =WAN-OUT
/ip firewall address list
192.168.10.20=B
192.168.10.142=B
/ip firewall mangle
add chain=prerouting src-address-list=B action=mark-routing new-routing-mark=to_WAN1
/ip firewall nat
add chain=srcnat out-interface=WAN1 action=masquerade
add chain=srcnat out-interface=WAN2 action=masquerade
/ip route
add dst-address=0.0.0.0/0 gateway=192.168.2.1 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=192.168.1.1 routing-mark=to_WAN1 check-gateway=ping