Edited- I switched up an FPT/MPT but the links are all still good. High recommend Brewer's Hardware. Prices are the best in the business- I compared every part on every website imagineable. Customer service is even better.
Are you talking about the Ace Rotomold tanks? I have six of the 110s, and the part number for those (at tank depot) is A-INFD110-30. You need the full drain (FD) version, with the stand part no A-IN40/85-ST (http://www.tank-depot.com/productdetails.aspx?part=A-IN40/85-ST)
The racking bulkhead part number is FAA050PB, and you'll need a 38mm (1-1/2 inch) hole saw to cut the appropriate hole
Into that, you would screw a 1-1/2 in triclover-MPT adaptor http://www.brewershardware.com/1.5-Tri-Clover-X-1-2-Male-NPT.html
and attach to it a triclover ball valve (pick your favorite, there are lots of options for this) with appropriate clamp and gasket (I prefer the flanged EPDM gaskets for cold-side)
For the bottom, you need a 2" MPT to 2" triclover http://www.brewershardware.com/TC20M20.html
To that, clamp a 2" 90deg elbow with the appropriate clamp and gasket http://www.brewershardware.com/2-Tri-Clover-90-Elbow.html
and to that, add a sanitary butterfly valve http://www.brewershardware.com/2-Tri-Clover-Butterfly-Valve-Pull-Trigger.html, again, with more clamps and gaskets. On the end of that, you'll need a 2" cap http://www.brewershardware.com/2-Tri-Clover-Cap.html
Oh, and I really really suggest drilling out your stand caster holes to 1/2" so you can put these on: http://www.mcmaster.com/#catalog/119/1343/=ne60wx
Makes moving them around much easier.
You'll need a good bit to go through that 1/4" plate steel, though.
I haven't decided yet, and I may not even use one but McMaster has such a huge selection of O-rings I'll probably just measure it and get something appropriately sized.
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