When using a plastic cat litter box it is best to use plastic bags to scoop the feces and urine into on a daily basis and then putting in the trash. You should scoop at least once a day and more if necessary. You should never flush the cat litter down the toilet, especially if it is the clumping kind as this can cause an overflowing toilet. It would be good to have a covered container by the cat litter box.
You should have a good scooper to use to clean the cat litter box at least once a day. You can use a plastic scoop, but sometimes a metal scoop would be a better choice. And by putting it in a plastic bag and having a covered container you will keep the smell down. Depending on how much litter you keep in the cat litter box will determine how often you will have to completely empty the litter box and clean it. If you have a larger enough box where none of the feces or urine touch the sides or bottom of the litter box the less often you will need to completely empty the litter box.
When you do empty the cat litter box you should wash it throughly with soap