Wow, just saw this post, sorry...been busy lately.

We went to home depot and bought all toilet flanges
and pvc fittings...it was all very inexpensive.
be sure not to use round or oval tubs as they are
harder to fit the flanges etc. You need straight ends.
Also if you can get
bigger tubs, say 50 or 60 gallons (then just use two tubs)that would even be better.
Remember, when we did ours in 1997, they're wasn't such
a big selection as there is now...the tubs we see now
are thicker and more durable than the rubbermaid ones
we used.
Be sure to pack the out sides of the tubs with dirt as water is very heavy.

Thanks. I never would have thought of toilet flanges! I did find some really big, really sturdy tubs that I'll be using. I just wasn't sure how to link them.