I want to cut a hole in a metal petrol tank.

[rustic]

I want to cut a hole in my boats' metal petrol tank, to fit a fuel gauge sender in.
The hole needs to be 43mm diameter.
I was thinking of using a rotary hole saw.

BUT:-
Saw + Metal = Sparks + bang

I thought I could empty the tank and fill it with water to remove ALL traces of petrol and vapour.
Then drill the hole even under 1/2 " of water above the tank, as long as I don't electrocute myself.

I looked on youtube, several people do similar, has any body tried this and survived.
The tank will be taken off the boat and done in the open.

While looking on youtube, I found this clip of a guy mig weding a petrol tank with fuel in it, he did put some carbon dioxide in it first.
So I don't trust many things on youtube, but this is suicidal..


http://www.youtube.com/watch?v=aOqgDaV8UR4

Health and safety would panic if they saw just some of the things he did


Any advice please.
best regards,
Rustic