Hi Al;
    Returning the fuel to the fuel line rather than the tank (thereby to the fuel suction), is I admit not ideal. Not by a long shot. However in some cases it may be a necessary evil that can (and so far has) been made to work. In most vehicles there is one tank, sometimes two so it is relatively simple to return fuel to the source fuel tank. Most airplanes also have 2 tanks and occasionally one, so returning to the source tank is again fairly simple and should be the first choice. where it becomes more complicated is when you have to manage 4 or even 6 tanks. It's difficult enough to come up with a simple, safe, light and affordable for the average home builder, way to manage selection of these 6 tanks, but to return the fuel to the source tank, would become a potential problem. Some builders simply return to a single tank which they draw down first then switch back to before it overflows, while others always drawn out of the same tank, and simply transfer fuel to that tank. Nothing wrong with that and it is ideal for many. Fortunately were not all the same, which is why were here on this list.

    My reason for 6 tanks is to increase range for either flights to remote areas with no fuel service or over long stretches of inhospitable terrain (like passing over my mother-in-law's). The plan of transferring fuel in my mind allows the distinct possibility of pumping precious fuel overboard whether it be from directly transferring fuel or via a fuel return to a tank that is not the source. There is also the possibility of failure of the transfer equipment, which would result in inaccessible fuel on board. Sure these are remote possibilities and could be lessened by the addition of various safety checks and devices all which add complexity and/or workload to the pilot. Not much but some. So I chose to try to implement a variation of a return-less system.

    Sure as you've said the failure frequency could be in the hundreds of hours, so in my short time it has been just fine, but still not proven. However what would be the incident frequency of lost or inaccessible fuel? More, less? I can't say, but I do know that if it happened there would be absolutely nothing I could do about it in flight, so I'd better hope that I didn't really need it. With my current system design, I have 2 facet pumps and 2 FI pumps that are plumbed in such a way that is fairly simple for fuel management, but also allows full redundancy in that any pump failure would not prevent me from being accessing fuel. The issue of vapour lock remains but the facet pumps 7psi of pressure has so far proven to be more than adequate for elimination of this threat. So if this were to happen at least I would have options to try to clear the vapour. Better to be able to do something than nothing.  Now with that said, I feel the chances of a vapour issue developing halfway through a flight are even more remote. This would be most likely to rear it's ugly head during the take-off you described after a long taxi and wait in the south Texas sun. Or in my case more likely while flying in mountain valleys when working it a little harder. Exactly the time I wouldn't want it to happen. That's why the facet boost pumps are always on at these times.

    So as Ed has pointed out, while millions of cars return the fuel to the tank, millions don't. But, I must add, most or all of them have a true return-less fuel system which we don't. Some of us are trying to copy that within the limitation placed upon us. Could we make it a true return-less system? Sure we could. At the low, low, price of a few more pounds and cost and complexity per tank. There is no free lunch here. Would I be willing to pay that price, while dead-sticking it down into a mountain valley. Of course I would, but using that logic would result in an ultimate safe plane, as it would never get finished. So here we are discussing ways to make it work without returning fuel to the tank. And I can say that it has worked well. I just can't say that it will always work well.
    I would never suggest to anyone that the way I did it is the best, but when asked about it, I'm happy to report my knowledge based on my experience along with any cautions based on that same experience. Then in the ensuing discussion I may learn something. Which seems to be the case here, as Charlie, who started this thread with his question has shown his idea based on what he's learnt from the discussion and it has his own subtle differences, with regards to regulator plumbing, that I'm surprised I overlooked and I think it has real promise. So much so that I'll consider a possible change to my current system.

    Other commitments these days usually restrict me to lurker status (that always sounds creepy), but the occasional questions directed at me usually don't go unnoticed and I enjoy the free exchange of ideas that happen on this list. I appreciate the words of caution, but when phrased as a command not to go against the grain, it loses it's validity as it is reminiscent of another place where free thinking is discouraged. We're all aware of the risks of venturing from the beaten path, which is why we're here to discuss, dissect and hopefully come up with a better way.

    Al, I do value much of your advice even if it comes across as harsh, but I figured I'd explain my mindset which I suspect is shared by a few others here, which is to minimize and take calculated risks, but not reckless risks.

Todd
C-FSTB