PG, holding tank work is the worst thing I have ever done, and I was putting a new one in where no man had gone before. Ie, I did not have to remove old one first. Of course, being a 1975 CHB, it was never fitted with one, and no such thing was ever envisaged, so no real space to put rigid plastic tank, so it had to be a Turtle Pack bladder type of 110 litre volume, = close to the 30 gal (US) you are doing. What I found the hardest was getting the tough white sanitary grade hose on far enough onto the various barbed connectors, etc. What did help was using a plumbers type silicone lubricant and heating the hose end to be put on with a hairdryer. Trying to heat it in hot water was hopeless, as it always cooled down too much messing about, and there was too much risk of spilling hot water on me, (in this case you), while working in a confined space. The hair-dryer saved the day. Best if like mine it was an old one superceded by the SO's newer one, as it will get pretty messed up with silicone and whatever. Removing the old will be fun, but at least you can just cut through the end attached to the old tank, bung it quick, and then deal with detail once removed. If you are re-using the runs from the toilet to the tank, just done cut any more off than you need to,and being new, and empty, you might be able to do the hose attaching in slightly less cramped quarters and then install it once done. Good if you can, but depends on the geomtry of the whole set-up. Best of luck with that anyway. I just pray every day that it will be ages before I have to again do anything to mine, as the memory of fighting that hosing still haunts me.
