Hi lporter868,
Welcome to the Heartland Owners Forum.
Has it ever closed completely?
It's pretty easy to close the valve on paper or other waste material, jamming it into the grooves that the blade slides in. If it's just a slow leak, you can use an external
twist-on gate valve at the sewer outlet so that the water doesn't leak out of the black tank and go down the drain, leaving solids piled up.
Repeated filling and flushing of the tank may help clean the valve, if that's what's wrong with it.
If it's a defective valve, you may want to have your dealer fix it for you.
Many of us dump the black tank, refill it, dump it again 2 more times to make sure everything is out, before closing the valve. A
clear adapter is also useful so you can see what's coming out of the sewer outlet. Here's one that also has a gate valve. With this, it's very easy to fill and dump the black tank more than once without closing the tank's gate valve.