I enjoy reading your posts and have a simple question. I recently replaced my "Y" valve though I am not sure why I did not just eliminate it since you cannot use it where my boat is. But nonetheless I did replace it and noticed that the old (1984) hoses were caked inside at least a 1/4 inch thick all around with hardened you know what! Here is my plan and tell me what you think. I want to fill up my wastewater tank with water to dilute all the old chemicals(Odorlos, Raritan Concentrate and who knows what) and then pump out. Then I intend to again fill with water treated with Kronan that I bought at the Houseboat EXPO. I will fill the lines all the way back to the bowl and let it sit a week. The guys at the booth said the bacteria would then begin eating all the waste and turn it into a slurry that could be pumped out but I may have to treat a couple of times. Now that stuff is pretty hardened in there because I had to scrape some out to fit the hose over the new "Y" valve so I cannot imagine this will work but it was only a $20 investment and I did not want to miss the chance for a quick fix. As for actually replacing the lines, I can do that if push comes to shove on the one from the head to the "Y" but I cannot disconnect the one connected to the tank itself without ripping up the galley floor and sawing out the plywood so this seemed like it was worth a try. Your thoughts.   

Since you've already bought the Kronan product, it can't hurt to try it...but if the hardened buildup is hard water minerals that are brown only because they're stained by waste, it isn't likely to do much good. If that is the case, a 12% solution of muriatic acid in water (be VERY careful handling it, and follow all directions for use carefully!) will clean out the hoses in a hurry...so will undiluted white vinegar, but vinegar takes longer and may require repeated applications.

All that said...if it were my boat, I'd replace 20 yr old hoses...'cuz the buildup is likely be the only reason they don't stink...it's providing "insulation." I know it's major PITA to create access to the tank...but all hoses have to be replaced sooner or later, and if the tank is _meta_l, it will have to be replaced too...So the hatch should be big enough to allow the whole tank to pass through it and provide access to ALL the tank fittings...'cuz just replacing the head discharge hose is like washing only half your face...if one needs replacing, they all do.

As for cleaning sludge out of the tank...if it's turned to "concrete," nothing will dissolve it that won't also damage the tank. But if it's still "mud," all you need is clean water...but filling up the tank won't do it. What will work is a few gallons at a time--enough to cover the bottom to 6" or so--down the pumpout ('cuz that sends the water into the tank at the bottom so it can stir up the sludge)...pump out...repeat...repeat...repeat...till you're only pumping out clean water. It can be time consuming, but costs nothing.

This should be done at least once a year.

Once you've solved the problem, you want to prevent it in the future. If the buildup really is just waste and not mineral, it's obvious that the toilet isn't being flushed long enough to move bowl contents all the way to the tank, much less long enough to rinse out the hose behind the waste (If you're sure the toilet IS being flushed long enough, the buildup has to be mineral). If your concern is filling up the tank too fast with flush water, at least put a couple of quarts of clean water down the toilet once a day, and especially when the boat will sit for several days. To prevent mineral buildup, follow the clean water with a cupful or two--no more than that--of undiluted white vinegar.

Fwiw, I think you'll find the _link_ in my signature very useful, not only for curing problems, but for preventing 'em.