[prestadude]

Like Larry B., I redid the entire watewater plumbing. On mine, the air valve was working but the second, manual valve would not move more than an inch. I ultimately had someone come in with special cleaning equipment, drilled a hole in the ABS elbow for access, and forced the manual valve partially open (I have some pictures on this operation under another post regarding a clogged wastewater tank). After the tank was clean, I cut out the old plumbing and found that the rubber seal on the manual valve (Dupree brand) had been installed backwards so the buildup of head in the waste tank displaced the rubber seal causing the valve to jam.