Unfortunately...
and to be honest and fair, Peggie -- this time -- is just about 100% right about "concrete" sludge in the bottom of a holding tank (I can't believe I'm actually not only agreeing with her, but validating what she is saying!! Sheeeesh!!) However, to be fair, in more than 30 years in the family business of running the largest private campground on the Miss. Gulf Coast, I've seen the problem innumerable times. It's true; if sludge in a holding tank hardens, there's little hope of salvaging the tank. It was always a helluva lot easier to replace the tank than try to "unload" the old one. She's also right (sigh!) in saying that there's really not anything out there that will dissolve hardened sludge.To answer the main question about how to get the tank out of the space, ever hear of a jig saw? You're gonna have to enlargen the hole to remove the tank, install the new tank and then epoxy some "rabbetts" around the edges of the enlargened hole and cut a larger cover board. Not all that hard actually.The idea about installing a 4" access port in the top of the existing tank is a good idea, too, and it's what I did on mine just as a precaution. Again, it's not all that hard and takes only about 30 minutes to cut and install the port and about 24 hrs for the 3M 5200 to cure. It's a worthwhile project, especially if you don't like the idea of replacing your existing tank. Just get you a hole saw, a watertight inspection port, a tube of 5200, three clamps and go to work.Peggie's also right (here I go again) in that holding tanks require more periodic maintenance than just pumping them out. One might also consider NOT using toilet paper in them. Use TP, then put it in a sealable plastic bag and dispose of it in the trash (if at sea and beyond the appropriate limits, overboard! Bet that'll set the Tree-Huggers off!!)I'll disagree with Peggie's comment, tho, about the muriatic acid not affecting the "chemical" in the holding tank than she inferred binds the sludge and toilet paper. Holding tank chemical -- of which I am a proponent -- has no adhesive, binding qualities in and of itself. It's the sludge and it's actual weight and the fact it dries as a solid that albeit "glues" itself together that causes sludge to become a solid per se. Drop by my former city's treatment plant there, Peggie, and I'll give you a quick tour of belt presses and drying pits!And, just a recommendation to you, too, Peggie. Look, in a sense, you've taken some hits from folks -- probably me, included -- not so much critical of your expertise, experience and knowledge of marine sanitation...which, actually, in this particular area you're more often right than wrong...but your delivery! Sometimes, it just kinda comes across you think the rest of us don't know much and maybe we don't, but nobody likes having that pointed out to them!!! Least of all me; hell, I know I don't know all the answers. You must know something about what you're doing and you must be doing something right because, heck, none of us have ever sold our businesses to a much larger marine supplier such as Raritan!I read all the comments you made and you were pretty much, as we say in flying, "dead nuts" on the ball. But, hey, Peggie, how about more about how to solve the problems we all encounter rather than tell us what we did wrong that got us to this point? Sure, you seem to have some pretty acute diagnostic skills as to what caused the problem, but what most folks are looking for here is how to solve the problem...'cuz they probably got a good idea of how to prevent it in the future...and that's where your experience is of the most value.With Olive Branch extended,Bob