iptables service with debian

[Muhammad Yousuf Khan <sirtcp@gmail.com>]

i run this command

iptables -t nat -A POSTROUTING -o eth1 -d 8.8.4.4 -j MASQUERADE

my client computers able to ping 8.8.4.4

but  when i "iptables --flush -t nat"  it clrear the table but my
client can still ping the destination.
i check "iptables-save" is shows that tables are empty.
 i thought that there could be some kind of service related to iptable
 in /etc/init.d  folder so that i can restart that but there are none.
and i notices after 5 minutes or so my clients computer were not able
to ping which means my commands affects after 5 minutes.

but i want prompt effect of every iptable command. is there any thing
that can be done in this regard ? pls help

one more thing what could be done to retain all the iptable statements
even after reboot. i think writing all the iptables command in
rc.local
is not a good idea. it is work around.

can any one plz help in this regard also.

Thanks