You have to run the tanks down dry almost, then re fill with fresh mix. Otherwise, the tank will eventually start to get over rich with oil.
Two years now on the same 15 gallon tank and no richness in oil is evident when running a 1957 Johnson 35hp. The tank has never been run empty and has never been drained. Mix ratio is 24/1 not counting what the recovery system adds. I’m sure I’ve run at least 200 gallons through this system.
Something I never see mentioned is the capturing of the gasoline/oil mix vapors that get pushed through the crankcase drain valves after the condensed liquid fuel has passed. If it is sent to the tank then the tank vents it to atmosphere. I vent the separator to the air box. At idle a plume of vapor about a foot long and several inches in diameter can be seen coming from the fuel line that runs up to my air box when it is disconnected.
For over two years now I’ve been using a water/air separator designed for use on an air compressor.
Here is the vapor line going to the air box:
