The uniflow tank was invented by Edme Mariotte of Dijon, France, in the 1600's. A search for Mariotte Siphon or Mariotte Bottle will turn up more information. For example: http://www.uswcl.ars.ag.gov/exper/mariotte.htm Basically a uniflow or reguflow tank gives uniform flow in spite of changing fuel head. I do not know the the physics involved but I have success using the idea that the engine thinks the fuel is coming from the uniflow outlet in the tank. Many who use a clunk tank in control line tie the two clunks together. I've used uniflow tanks for many years in control line racing and stunt airplanes, with and without pressure, with great success. I would not build a serious airplane without a uniflow tank.

Incidentally, Edme Mariotte was the first person to test a model in a wind tunnel.

Jim