Changing the litter BOX (not the litter inside the box)

How often should you get a new litter box. I mean actually throw away the box and buy a new one. I scrub it once a week, but there are some stains on the plastic that do not come out. I'm wondering if there is bacteria that I cannot clean.

I've had this box for 2 years, and 2 cats use it.

Any insight would be great!

Soak the bottom of the cat box with vinigar. This should remove any stubborn stains. After rinsing it really well, soak it in hot water with bleach. (The bath tub or empty trash can is good for this) Rinse it well and allow it to air dry. Spray it with Pam or other non stick spray and it should last quite a few years more.

thanks!

Thanks for the advice.