#view current chains
$ iptables -L

#remove/flush all rules & delete chains
$ iptables -F
$ iptables -X
$ iptables -t nat -F
$ iptables -t nat -X
$ iptables -t mangle -F
$ iptables -t mangle -X
$ iptables -P INPUT ACCEPT
$ iptables -P OUTPUT ACCEPT
$ iptables -P FORWARD ACCEPT

-F : Deleting (flushing) all the rules.
-X : Delete chain.
-t table_name : Select table (called nat or mangle) and delete/flush rules.
-P : Set the default policy (such as DROP, REJECT, or ACCEPT).