For each printer, I have 1 resin tank for each resin I use. Personally, I would rather pay for the convenience of quickly switching resin tanks, instead of thoroughly cleaning the tanks to switch between different/incompatible resins.
For example, my primary printer use is for generating aligner models. So, I have 1 tank for Die and Model Tan for each printer. I also use the printers for IDB trays. Since, the IDB (and Splint) resin is FDA-cleared for long-term use in the mouth, and general-purpose aligner model resin is not, I do not want to waste time cleaning tanks and switching resins. I’d rather just quickly switch the tanks with different resins already in the tank. So, I also have a separate tank for IDB resin. In addition, I do quite a bit of beta testing. So, I also have a separate tank for testing resins.