Just a suggestion for a quick fix
I think Don is right, you have a leak in the reservoir. I've tinkered with mine to get all vacuum valves to work properly. I think if you pressurize the holding cell with compressed air, (don't get carried away now), you can probably do a soap and water leak test on the holding cell. A little JB weld on the leak if you find one will probably fix your problem. If you find no leak please respond back for additional help.