Although prior to painting I pressure tested the tank to check the welds the best I could with what I had.
Anyway after pouring in the first 50litres and constantly checking the underside of the tank for leaks, all is looking good
As it turns out there is a pinhole in the top of the tank where the spare tyre sits. I initally stripped all the paint off the tank and saw the slight skale rust on the top and cleaned it up. All looked ok with that. Didn't even think to check that area when I was leak testing due to being so concerned with my welded repairs.
O well as they say shit happens.
Woofto Car Club Member No4