I run mine for a week- it's a 1 gallon, and we make 2 gallons a day.
Every Monday (our day off), I run it with a generous splash of white vinegar (probably 1/2 c) and water past the full line, with the top off, for a few hours. Then I scrub it and rinse.
This has worked well for me the last 9 months or so.
Now I need another distiller as I've realized I can't produce enough water for my family of four, plus pets, with only one in the warmer months!