The drainage rates in biofiltration devices are usually controlled using an underdrain that is restricted with a small orifice or other flow-moderating component. These frequently fail, as effective orifices that are used for flow control are usually very small (< 10 mm) and are prone to clogging over time. The main goal of this study is to evaluate the performance of a foundation drain material (SmartDrain™) under a variety of challenging conditions. SmartDrains™ work by capillary action, requiring very little head to initiate flow through the use of a siphon. This paper will present the results from a series of tests conducted to determine the flow capacity and clogging potential of the SmartDrain™ material during biofouling experiments under controlled pilot-scale biofilter conditions. A pilot-scale biofilter that consists of a tall Formica-lined plywood box, 0.90 m by 0.85 m in cross sectional area and 1.20 m tall was used for the tests. The tests were conducted using two different species of green algal that were encouraged to grow in the biofilter device for several weeks before draining. The results indicated that the biofouling had only a small effect on the discharge rates, even though the algal growth was extensive. Prior tests evaluated the SmartDrain™ performance after excessive loadings by fine ground silica particulates (Sileshi et al., 2010b) and also for a range of length and slopes using clean water (Sileshi et al., 2010a).