Hi Bob,
I run the same clunk on my N7, it is a bit of a fiddle to get it in the tank but it will go in with a bit of encouragement, I found the best way is to angle the clunk slightly and feed it in bit by bit then it will go in.
The silicone O-Ring on the clunk prevents the sintered material of the clunk from rubbing the inside of the tank, it is not a huge problem to run the clunk without the O-Ring but over time you will be able to see where the clunk has rubbed during flight.
Hope this helps,
Cheers,
Ross