Guys, we've discussed this before. So, let me reiterate what I said before, and add a new trick I've discovered for starting my '57.
First - it is NOT POSSIBLE to siphon an original tri-five carburetor dry. The drain back you describe is not possible because - on all tri-five carburetors, the needle and seat are located in the air horn (top cover) above the float. That means they are also above the fuel level in the bowl. If you attempt to siphon the bowl dry, all you're going to do is suck out air - not fuel. So, unless you've got a cracked fuel bowl (and if you did, you'd know it!), the only way you can end up with an empty fuel bowl is evaporation.
However - it is ENTIRELY possible to have a fuel pump that works properly in all respects (proper fuel volume, fuel pressure, no external leaks) where the check valves do not seal 100% perfectly. If the car is parked pointing uphill, fuel and/or air will slowly leak past the check valves until the pump and fuel lines are empty. Then, when you try to start it, the pump is sucking air for several seconds before pulling the fuel in. (Think about what it takes to start the car if you refilled it after running out of gas.) On the other hand - if you park the car pointing downhill, the line from the tank, the pump, and at least part of the line from the pump to the carb remain full. Now, it'll start pretty quickly, even with a bone-dry carb bowl.
Finally, my latest trick for starting my '57.
Believe it or not - my '57 with my WCFB will start much faster if I DON'T pump the accelerator at all. Yes, that's right.
Suppose my '57 has sat for 1-2 weeks. If I press the accelerator just far enough to set the choke - about 1/4 to 1/3 down - it'll start almost as fast as if I'd driven it earlier that day. I'm talking under 5 seconds to start. It'll start faster than my modern cars if they've sat for a few days.
If I press the '57s accelerator to the floor once, it'll take longer to start. If I press the accelerator to the floor twice, it'll take even longer to start. It'll also run rougher when it does start.
Also - I switched to using nothing but ethanol-free gas in my '57 over a year ago. That's the first thing you need to do if you haven't done so already.
