250 miles from a tank.

[stevierst]

Just wondering, but what about swarf or filings in the tank after drilling?

I used a cocktail umbrella, closed it up, placed it through the filler neck and opened it up, taping it in place whilst I drilled an 8mm hole where the already puny 3mm hole is. Once the hole was done,  closed the umbrella, and removed it from the tank with swarf in it. The tank takes another 2 litres now.
Yamaha realised how long the neck is, and reduced its length for the 2k model. (hence its 2 litre larger tank)
You need not worry too much about crap in your tank, have you ever emptied the fuel tank on a 10 year+ bike, there's normally all sorts of crap in there cleverly filtered out by gravity and the mesh filter.