Going back to my original post on this thread I have finally nailed down the issue with my pomp-out woes.
After replacing the vent hose (not the problem) I closely inspected the y-valve installed in the system. Originally, the y-valve was intended to allow
overboard discharge but since I'm in the Great Lake that is not allowed. So, I've been trying to
pump out the tank for the last three years.
The tank would NOT
pump out with the valve in either of the two positions, but would allow it if I turned it half-way. At first, I thought the problem was due to the flimsy nylon vent hose collapsing under the extreme vacuum of the pomp-out.
But the problem persisted after I replaced the vent hose. Finally, I had the time to address the y-valve and after close
inspection I confirmed that they had installed the y-valve wrong!
In one position, the y-valve connected the
holding tank to the
overboard discharge. In the other position it connected the pump-out to the overboard discharge! So, that meant that the pump-out had NO direct connection to the holding tank!
Another issue that I saw in the system was that the y-valve was installed in such a way that it could have created a syphon action from the
holding tank toward the overboard discharge. That would mean that black
water could fill the hose from the holding tank all the way to the thru-hull and stay there since that seacock would never be used in the Great Lakes!
Before I launch this spring, I will have to break the seal on the overboard discharge and make sure that line is empty before sealing it again.
I cut about 10 inches from the pump-out and holding tank hoses so I could move the y-valve higher to prevent a syphon.
So, the moral of this story is that you should NEVER assume that any device on your
boat was installed correctly by the manufacturer and especially not the previous owner!