How often do you clean your half gallon fish tank?

I personally would empty it, then scrub it clean and use it occasionally as a flower vase. It is not large enough to keep any kind of fish in properly. The basic rules for keeping fish successfully are. :- 1 inch of fish needs at least 1 gallon of water (a Betta is a 3 inch fish). Every tank must have a permanently running 'cycled' filter. Every tank must have at least 50% of its water replaced every week.

The above is not completely true. A Betta in a half gallon tank should have half of its water replaced each week. You should use a conditioner with that water (mine came with Nutrafin Betta Bowl Water Conditioner). I also make 20% of it HBH Betta H2O, which can be bought in bottles.