Why nothing serious? is it a second job? I think you need to be serious to start a business.
Apparently, with wheelie bin cleaning, you can tip the dirty water you creat from cleaning the bins, down the drain so you ither need to recycle it with an onboard machine, or carry it in a waste tank and dispose of it appropriately. If you carry it you need a waste carriers license. you also need some other license i believe.
Somehow i dont think wheelie bin cleaning is going to be the business to start if your looking for ''nothing serious''