Usually I’m doing two vents with use of saddle tanks, better ventilation and just in case my tanks don’t filled evenly I can close one vent to fill the other one until level is equal, plus I never do overflow lines underneath my jet just because one’s I clogged one up with sponge that was under my jet for transport, from that moment the vents are on the lower side usually at 30-40 degrees, much easier to plug overflow tank , my vents are at least 6-8 mm lines and never smaller, remember if uat is collapsing it means vacuum that means fuel or air vents restriction!