I wouldn't say it's good, I'd say it's as good as it's going to get. Concrete grade height and street height mean I only have what I have. It falls the whole duration, even it it's down to .3* in a few spots. I borrowed some help to make sure. Water seems to come out when I dump it in at the top. For the 400sqft of roof it's attached too I've got way more flow rate than needed and if it backs up during a 25 year storm, I just have wet ground. The entire purpose was just to keep the watershed from the roof off the side yard and send it to the street because during late fall and winter, that side of the house only gets a few hours of sun a day. I lost a whole month building when we got a few storms back to back as the clay was so saturated you couldn't drive tracked equipment on it and it just wouldn't dry out.