Help!!!Gray Water Tank "Sludge"

We have a significantly blocked gray water tank. Think the previous owners lived in the unit and didn't properly use/service the tank. I thought I had completely drained the unit before winter layup and that my sensors were just clogged (showing full tank), but apparently went through the winter with a full tank.

Virtually nothing comes out when I open the drain valve. Since the valve and pipe are fairly small (compared to the BW), I can't get any kind of flush stick up the pipe. I have been able to get about 15' of a snake up there, and a water hose (but only about a foot because of a pipe bend), and what comes out appears to be pieces of a chalky white substance, about 1/2 to 1 inch in size. When touched, it crumbles apart. I'm thinking that enough comes loose that it starts to drain, but clogs the pipe until I run the water back through it and them some more comes out before clogging again. It doesn't look like grease; I'm baffled as to what it is. Does anyone have any suggestions on how to break it up or emulsify it with some sort of chemical that won't hurt the tank or drain pipe/valve???
Help!!!Gray Water Tank "Sludge"

Did see this once before. On a neighbors coach on which we used a semi-hi pressure washer and sealed it into the drain with a towel. The resultant pressure broke loose the clog. After three times of doing this, we heard the water sloshing inside the tank. it then flowed free. His coach sat for four years without use which may have contributed to this. However it was last parked with the grey tank half full. I am not recommending anyone else try the hi pressure routine as it may blow apart a poorly cemented seam. Happy Motoring, Butch - Nancy Lake, Alaska
Help!!!Gray Water Tank "Sludge"

Thanks Butch. I have a 2300lb pressure washer and I have thought about using it, but I'm afraid that I'll bust something up in an inaccessible area and create another problem. Unfortunately, the tank itself if not visible, only a few feet of the drain pipe. I'm soaking some of the crud in Drano right now to see if it has any effect. Thanks again.
Help!!!Gray Water Tank "Sludge"

Spent a lot of time on this yesterday. Culligan guy thought it was scale and recommended muriatic acid. Got a gallon, and tested a piece of the stuff in an undiluted sample of the acid. I thought it would immediately bubble up and dissolve; wrong. It's been about 18 hours now, and the stuff hasn't dissolved, but there are a few dead bugs in it. So far, no chemical, vinegar, or baking soda has touched it.

The good news is that with repeated back flushes with a water hose attached to the drain cap (until it backed up in the shower), I have been able to completely empty and refill the tank with fresh water four times. I just kept at it and I get fairly clean water out, and a few of the chunks of the stuff come out each time, mostly when the tank is almost empty (one piece was about the size of a small hotdog). I used the snake a couple of times attached to a drill to try to break the stuff up; however, I still think there's a lot of it up there. Regardless, I think the problem is mostly solved, and if we are at a dump station and nothing comes out, if I start the backflush routine, I think I'll be able to get it started.

The only thing I haven't tried is the enzyme treatment, so I'm going to half-fill the tank, load it up with a treatment, and dump it at the next CG before parking Thank you all so much for your ideas.
Help!!!Gray Water Tank "Sludge"

Better try blue Dawn & warm water flush first. Then add about 4 capfulls of "Piranha" waste and sludge digester! Strong stuff that really works! Check it out as I did at