Hi Lowgear,
I bought mine from the local Home Depot, but that was a couple of years ago now and I couldn't tell you where the best deals lie at this point.
My tank has the one port near the bottom that is normally used to drain the tank.
There are four ports on the top... Cold in, Hot out, Pressure/Temp safety valve and the port that is normally occupied by the sacrificial anode rod which must be removed. (I didn't use this port and it is currently plugged with a 3/4 plug.)
On my tank all five ports are 3/4 NPT which made it simple to organize the plumbing. My system draws the oil from the bottom port to a chinese made gear pump and sends it back to the old "cold" port on top via a glass re-enforced clear tube. Enroute it passes through a manifold that allows me to either pump out oil or draw in the Methoxide. The pump is driven through a flex coupler by a 1/3 HP motor. Also found on this manifold is a cheepo automotive temperature guage sender to lets me keep track of the working temp of the reactor.
The old "hot" port has a "T" plumbed in where the vertical port is used as a gravity port to introduce the Acid and alcohol for the Acid/Base two stage process that I use. The horizontal port is home to a pressure gauge that allows me make sure I don't exceed the safety margin of the plastic hose mentioned above. I let my system pressurise to 10PSI then the heater switches off. This is a 100% safety margin for the hose I use.
The old "safety" port has a "T" plumbed in that has the original pressure/temp safety valve screwed into the vertical port and a nipple that fits my compressor hose in the horizontal port. I use this port to lightly pressurize the tank to aid in draining it.
I disconected the upper heating element as there are times when it will be above fluid level... and I really don't need the exitement that might follow an electrical heater burning out that is exposed to alchol vapour at 160 degrees F.
There are lots of shut-off valves in my system that allow me to completely seal the tank if needed.
If you go this route be sure to remove the 1.5 meter long thinwall plastic pipe that you will find inside the cold port before adding your plumbing.
I hope this helps, feel free to PM me if you need more info!
R.