My first “rig” I used a barrel as a buffer tank. It was cheap, but it definitely had its drawbacks. They’re hard to secure properly due to the shape (and also aren’t terribly space efficient for the same reason).
You can only install the float valve so high, or the outlet bung so low. So functional buffer capacity might be closer to 45 gallons or so. You can increase that slightly by installing an elbow on the back side of the outlet bung to draw down a little lower. And I suppose if you got creative with the float valve, you could cut a hole to fit the hudson float to stick up out of the drum.
I found an open top drum with a lid to make installing the plumbing easier. I know some who’ve just cut a hole in the top of a closed drum though, and just patched up the hole afterwards.
Edit: here’s how I have my tanks plumbed now: Infinity Cleaning Mobile 3.0, aka Truck Norris - #434 by Infinity
And a view of the float valve: Infinity Cleaning Mobile 3.0, aka Truck Norris - #326 by Infinity
