Clarifier effluent troughs - How to design launders I overflow weirs

[@jasonvoorheis1984]

Thankd

[@salahalmafrjy2095]

Hello, if I have a rectangular laboratory sedimentation tank and I want to take samples from inside the basin, how much do I go down from the surface of the water to take a sample and why? I have been told to follow something but I don't know why?