The problem with using an exterior filter for the lint especially in the summer, is that the main tank doesn't get rinsed that often, when the bacteria builds up especially after a job with let's say pet problems/incontinence problems/messy tenants,the stench yes stench rather than smell can be unbelievable and not a very good advert for your cleaning business, so as previously said it's a good idea to rinse your waste tank on a daily basis, and while you're about it you can empty the internal lint basket.