Using a check valve on the went line defeats the whole purpose of the uniflow tank system. As been previously stated, when the trottle is reduced to idle or low rpm after high speed running the pressure inside the tank will be maintained at a too high pressure for some time causing the engine to flood.

The uniflow tanks were developed for control line flying many decades ago. At that time the went was not connected to anyting, but ambient pressure. This resulted in a constant pressure head that the carburettor had to work against, resulting in a very constant engine rpm.

The principle itself is much older than this. It is known as known as Mariotte´s bottle (namned after the French physicist Edme Mariotte (1620-1684)).