P0442 Evap leak question

I have had my 360 for a bit over two years now and it has been trouble free. However, recently it keeps poping up with a Slow Evaporative leak or P-0442. I have a Evap tester machine that applies smoke and reads off pressure along with a ultrasonic tester. However, I do not have the adaptor to hook it up. I was thinking about teeing off of a line but not sure which is the best to hook to. The gas cap would be the best but as it is a 60mmx2mm thread, nothing real common works. Looks like I have two choices, 1: try to find a junction to splice into or find a used cap and make an adaptor (best choice in the long run). If anyone has a junky cap off that will fit, I would love to help you find it a new home. It looks like it could be an earlier 355 cap without the vent as I am going to have to modify it anyway or a 360 any year. Obviously, it does not have to appear anywhere pristine or even have a seal inside. I am also open for any other suggestions. FYI: the current cap holds pressure and reliefs on vacuum as it is supposed to.

 

I am a bit Frugal also which is why I did not just take it to the dealer. A tapered rubber plug adaptor would work fine if the inside hole was round. I tried to locate a threaded anything to adapt. There is nothing at the auto store that matches. I will check out the PVC section at Lowes/Home Depot. Once I get an adaptor, I have the proper equipment to do the diagnosis. Thanks for the response.

 

A follow up. I hooked up the tester to the larger pipe on the carbon canister and let the tester do it's thing. Using a ultrasonic tester with a long probe, I found the left rear rollover valve had a crack in the plastic where the hose connects. The access plates under the top are not for the rollover valves but rather the fuel pump/sending unit. The tray that the top folds into needs to be removed or at least lifted up to access. Once the rollover valve was out, I found a metal tube that was a nice tight fit and with some sealing glue, put it together and it is now stronger than new. After 50 miles, the readiness codes said it was ready and I now have an emission sticker and no engine light. About 2 hours work and virtually $0.00 in cost. I have found that the Ferrari's are easier to work on than Jaguars which are my speciality. Very surprised and pleased about this.