Last weekend my Grey Tank began talking to me when I was draining it. Started gurgling and shaking and making all sorts of noise. This is a new problem...has worked fine for two years! I looked at the vent pipe on the roof. Appeared OK...stuck a tape measure down the tube it did bottom out but came out dry. Felt like there might be a screen or something at the bottom. The Galley tank also had the screen or whatever at the bottom but it works fine. Left the Black tank alone! Can I shoot water down this vent tube with a hose and not have to worry about flooding my 5ver? Any other ideas?