I said the main purpose is to seal but also to stop swarf due to the fact that the inside of the tanks are not fine surface but have a few rough ends.
I personally disagree that sealant would not stop SWARF as sealant can be up to 10 mm thick.
I am sure some gets away but ae are talking about amounts that could block fuel here so I am sure hat the SWARF did not come form the tanks walls.
At least this is what i was taught at uni doing my B1 lisence.....but i see we agree on the low pressure indication....