Apologies if this is a bit basic, but as you'll see from the pic I have a small pipe coming from the fuel tank, do I need to put a hose on this as I'm assuming when I actually get to drive it the fuel will come out of it... if I do need a hose where would the other end go to stop the fuel spilling out?

(Cables are only this messy as I'm running them all before cutting to size  )

Just plug it and fit a vented cap.

You either need to get the opening much higher than the tank eg uup the windscreen pillé, or fit a one way valve

Or what David says

If you have a sealed cap put a hose on it but it needs to be long enough to go up to the top of the dash across the buggy then forwards and out under the front of the fuel tank to stop surge spillage.

I had a good play with that pipe on my build thread

https://www.beachbuggy.info/index.php/topic,20.msg91535.html#msg91535

If cap is external vented cap is simplest and avoids the risk of fuel sploshing out
If the cap is under a bonnet then a vented cap risks vapour build up so a vent pipe is better but has to be routed to avoid fuel leakage with acceleration, cornering etc. I've run mine out into a front wheel arch with a valve that allows air but not fuel to pass. Valve is not cheap but you only ever need to buy one, got mine from Demon Tweeks designed to stop fuel spillage if a race car is the wrong way up

In the garage today.... where else  ......  Two things caught my eye because I had read this thread a few days ago.. As they say " a picture paints a thousand words". I have mentioned this before but for those who have joined the forum since then I will relate things again. In the 53 years that have passed since owning my first car I have only ever seen two petrol tanks implode. The first one was a new Opel Manta leased by my boss and he and I were driving along the motorway when the engine showed all the signs of running out of petrol despite the fuel gauge saying otherwise. Luckily this occurred when we were approaching the service area so the car coasted in and up to the pumps. Weirdly. it seemed at the time, the pump shut down when only a small amount of fuel had been put in. Looking at the tank showed that it had collapsed inwardly almost completely. Was a leased vehicle so it was taken away for repairs. When the vehicle was returned the report stated that although new the breather was found to be completely blocked. The second vehicle was much earlier but I cannot recall much detail now...

Having said that tank collapse only occurred twice over this period it does show the importance of a fuel tank breathing ability....  It is quite  something to see the effects of temperature on petrol even with modern E5 rubbish. A breather doesn`t just prevent a vacuum being able to form it relieves pressure during expansion. Here is how important that can be....

1st photo is of a standard 5 litre fuel container I use to top up the lawn mower. This was opened to top the mower up last week so the inside/outside pressure was equalized at that point. Container about 1/3rd full. Over the last week the garage temperature drops to around 10 degrees C overnight. Warms up a little during the day. Outside temp during the day has been mid teens...
Look at the shape of the green container. Cap was put back on last week after container had stood in the sun. Note how the container has sucked in, (imploded due to the temp difference). The black screw on top should be level. Look then at the other image of the bottle containing E5 petrol. Firstly in the garage with it`s sides sucked in and secondly after it had been outside the garage for approx 30 minutes. Cloudy day, no direct sunshine, but much warmer than in the garage. Petrol gasses in the higher temp and bottle expands back to normal shape.

Now then there are many views of how a breather and it`s pipe should be fitted, placed etc.......  This next bit is just my view and my experiences with my buggy. My tank take off is a little higher than that shown earlier in this thread but not much. I fill the tank with exactly 30 litres of petrol. This leaves an expansion space within the tank. I have the breather pipe leaving the tank space area on the offside and the pipe is secured down the tub to the frame head base close to the master cylinder area. Then through the existing hole to the underside therefore venting to the underside of the frame head section. In addition I have a standard one way/ anti roll over valve fitted as this was an IVA requirement. However I have run the buggy about rigorously without the valve to see if any leakage occurred and it didn`t.  Couldn`t get it to auto syphon no matter how hard I tried.(Valve now refitted).

During IVA testing the buggy was steered, heavy braked, rocked about in an alarming fashion by both myself and by the examiner so that he got a view from within and without. and at no time did petrol issue from the breather. The petrol must have swirled about so much that it was dizzy   

So.... just my experiences with my buggy so you can see that you can vent up above or down below tank.  The choice is yours

Brilliant example 

however, I wouldn't leave the fuel in a plastic bottle as it will eat through it over a day or two and can leave a dangerous puddle of fuel somewhere you don't want it to be   

Dave is right here.... Don`t leave petrol in polyester bottles it will eat through. See the discolouration of the E5 petrol. This is from the reaction with the bottle....   

Thank you all for the comprehensive responses and ideas, it's certainly made me think about my options for what I thought / really hoped would be a simple fix 

I've already chosen my petrol cap and cut the bonnet so I think I'll have to go with the idea of a one way valve.

Coul always drill a tiny hole in the cap, only needs to let air so can be miniscule and under the catch or whatever that is on the top so it can't be seen

Neil    ....  Don`t overthink this    ...  the solution is simple... All you need is to keep the fuel tank at the same pressure inside and outside. As Doon says a simple hole will do the job. You don`t need to install a one way / roll over valve. A Beetle never had one. In my case it was a "belts and braces thing for IVA..... 

Thanks Paul & Doon - again, much appreciated 

I started looked at one way valves and the price variance is crazy as I've no doubt the quality is too!

https://www.demon-tweeks.com/uk/mocal-in-line-fuel-tank-breather-valve-23340/ for near as damn-it £50 to £5 on Amazon...

I like the idea of a small hole under the latch, that could be the way forward, cheers guys!

Quote from: neilpop on May 15, 2023, 10:45:12 AM
I like the idea of a small hole under the latch, that could be the way forward, cheers guys!

Strongly advise against that one as when the fuel is used and you get negative pressure in the tank, it can actually draw any moisture or water through the hole   

Quote from: Dave DND on May 15, 2023, 11:21:37 AM

Quote from: neilpop on May 15, 2023, 10:45:12 AM
I like the idea of a small hole under the latch, that could be the way forward, cheers guys!

Strongly advise against that one as when the fuel is used and you get negative pressure in the tank, it can actually draw any moisture or water through the hole   

Good point but surely only if the hole is at a low point or it's really chucking it down. Depends on the orientation of the filler as well if it's at the centre of the bonnet and flat then risky as it could get a puddle but would it work if it's more of an angle? How is it really different to a vented cap and hole can be miniscule