Unless you plan on making inverted flight the main part of your flight program, a flexible feed line in these tiny engines is unnecessary clutter. They don't consume fuel fast enough to suck 4 inches of fuel dry before the fixed location feed line can get another sip of fuel. If you do mostly positive G type manuevers and flying, your engine will always have a trouble free source of fuel with a fixed feed line. You can still do some negative G flying with a fixed line, but it is best done when the tank is full. Flex lines in small tanks introduce yet one more failure point in the system, with next to nothing in benefit. I make the HAYES 2 oz tanks with a 3/32" brass tubing feed line that is hinged with a hunk of fuel tubing. The solid feed section is too long to swing forward on a hard landing and accidentally pinch the line shut. The SULLIVAN and DUBRO 1 and 2 oz tanks need a clunk that weighs half as much as the engine to swing the feed line, and these tanks are prone to pinching themselves off. With a diesel set up, learning how to make you own tanks from hobby store tin, 3/32" brass tubing and 50/50 solder is easy, and I kind of enjoy doing it. you can cut the tin with scissors, and form it around wood blocks. this way, you can make the tank conform to whatever space your plane might have allocated for fuel storage.