forget the valve, take and find a way to get a plain glass funnel into your gassing chamber- yes, you might have to change the chamber your currently using to accomodate- anyway, run the hose in, attach the hose to the funnel and lower it into the solution by about a 1/4 inch, this will allow the gas to bubble through, but when the suckback occurs, it can only draw so much liquid before the the vacuum is broken, self regulating. maybe not the most sophisticated of apparatus, but it does work.