Originally Posted by wayneskid
Does it "try" to close when you push on the switch? i.e. do you hear any sound of the mechanism trying to close the valve? If not, maybe you have a blown fuse?
In my Interstate manual, the manual override feature for the dump valves is shown on page G-16.
My 2012 manual has the same info, so it apparently hasn't changed. Fair warning, you'll have to crawl up under the Interstate to do the manual override. You'll want to drive the front end up onto leveling blocks to get more clearance underneath. That's safer than using a jack.
Side note, thanks to the macerator pump and the ball valve on the end of the discharge hose, it does no particular harm for the valve to be stuck upen for a while, as long as you don't add anything to the gray tank until it's fixed. Just a small drain on your house batteries for that LED light on the switch, which should go out when you turn off the battery disconnect. It would be much more worrisome if you discharged through a slinky.