The plastic tank that is inexpensive and commercially available makes the most fiscal sense, but we did make a mold for a custom tank which has over 1/2 a gallon more capacity. Our tank also has a sump, in other words a little popped out section at the bottom end of the tank for the drain fitting. This means we can drain ALL the liquid in the tank, because our drain is lower than the bottom of the tank, unlike a plain square tank with a fitting that takes up space and leaves some liquid un-drainable. So that 3 gallon commercial tank doesn’t really have 3 gallons of useful capacity.
Another feature of our tank is the hanger bolts are molded in. Drill three holes in the floor of the van (two for the bolts and one for the hose from the toilet), and put some nuts on it and you’re done.
But, it’s a huge chore to make the tank. We do a hand layup fiberglass cloth process, there are aluminum plates embedded in the top with the bolts going through. There are separately cast hard points for the fill and drain areas so they can be drilled and tapped for 3/8″ NPT, and probably half a dozen leak checks before it’s sealed. After the finished tank is popped from the mold, there is sanding, filling, leak checking, drilling and tapping, two access holes required for running down the internal seam have to be covered over, fill, sand, paint. It’s a day’s work spread over several days.
We can’t charge what it’s worth or no one would buy it, but it still seems like a lot of money even at this price. That Plastic Mart tank is just fine for $55
One of my sayings is “if a job is worth doing, it’s worth doing the hard way”. It seems like the easy way is never all that great. If you feel like I do and want maximum capacity for #1 collection, and want the convenience of the built in hanger bolts, then it might be worth the cost we have to charge for this tank.