Check Ronco Plastics
http://www.ronco-plastics.com They make top quality tanks and have more than 400 shapes and sizes, including over 100 non-rectangular.If you can't find on that will fit (which is HARD to do, but some people swear they can't), you can have a custom welded plastic tank made by C.C. Tech to any configuration you need. They're at http://www.gocctech.com/marine/boat-tank.htmOr, in your waters and most others you're likely to visit, consider installing a Lectra/San (CG certified Type I MSD that treats waste and discharges a flush a time legally in all waters except those specifically designated "no discharge.") instead. 'Cuz there aren't any "no discharge" waters of any consequence within at least 500 miles of your home port. Why store waste aboard if you don't have to? Especially when the alternative is not only more practical, but more environmentally friendly than holding tanks. You can read all about the Lectra/San on the Raritan website at http://www.raritaneng.com (from the home page, go to products, then waste treatment). List price is about $1000...but average discount price is $700-$750, which is only about twice as much as it'll cost you for a good quality holding tank, hoses etc. A lot of people here have Lectra/Sans and love 'em. That takes care of the waste management part. Now for the toilet...does the admiral demand the push button convenience of electric, or will she accept a manual toilet? The best "bangs for the bucks" for both are the Raritan PH II (manual) or the Raritan SeaEra (electric). You can check out both of those while you're on the Raritan site.