B192
Greetings -
Are we talking about an E35-2 or E35-3? If the 35-3, contact Ronco Plastics as suggested above - order the model B192. That's the hard plastic tank without the wing on it. Have Ronco mount the elbows on it using the butyl rubber - it will hold up far better than anything you can throw at it.
You lose about 1 gallon of capacity, but it protects against cracking at that joint (and you get a nice little place to store stuff for the system). See my article in the projects section about overhauling my sanitation system for more info...
Also - I strongly suggest having Ronco mount a 6" Beckson clear port in it (again, with butyl rubber) - so you can hose out the tank once a year and generally get access for problems, etc. Sounds unpleasant, but the benefits are pretty well documented - and keeps your boat from developing um, 'issues'...
//sse