[Madmax07]

We ended our latest camping trip yesterday. I was at the point where I wanted to flush the black tank. I hooked up the water to the sewer flush on the trailer. However, when I turned on the water it wouldn't go into the black tank. The hose was full of water and under pressure but it wouldn't enter the tank. I did notice that there was no (don't know the correct term) pressure release valve?? like there is on the city water inlet. Is there supposed to be one on the sewer flush inlet? If so, I would assume that is my problem. Otherwise does anyone have any other ideas? I still own a the same trailer seen in my profile. Thanks.