thanks. The main seal on the main cap is fine. The plated fittings that come with the tank require you to drill a hole for the vent line. There is already a hole in the front for the clunk line.
I have a slec fuel tank for petrol which includes the fittings. Here is the link https://www.slecuk.com/petrol-tanks-round
But it seems unusual that there are no o rings? Has anyone used these tanks without o rings.?