I agree with David,

in my plane (sealing tank compartment now) the black seal of the tank is much closer to the tank.

im pulling silicon tubes from the tank thords the fire wall, which has two tube diameter holes in it.

i had this kind of seal in my hobbico starfire, but it was going through the firewall, the tank didnt have the lip/chin.

its possible you got the wrong parts in tank kit.

is the tank with this black part sealed?

Alex