I am in the process of building a pond with a skimmer filter that will have a 3000 GPH pump which goes to a 100 gallon stock tank which will be used as a skippy type filter. I will be using 1.5" pvc pipe for the inlet to the stock tank and then I was planning to use 2" shower drains going to 2" pvc pipe as the outlet. The 2" pvc pipe will then go to a 18" waterfall weir with a opening for 2" pvc pipe. After reading these forums I am under the impression that I will need to have 2 shower drains for the output. So is it okay to have 2 pvc pipes leaving the stock tank which come together at a T and then enter the waterfall as one pipe. Will this work or will putting the two 2" pvc pipes into one just before the waterfall restrict the flow too much. I am guessing with a 3 foot head and the restrictions from the pipes that the output of the pump will be around 2000-2500 GPH. Is this an okay flow for this size stock tank.