Yup the whole system will run on the filtration and drip system of the 300. the pipe gos into one of the filter socks of the sump and the water going into the top 40b comes from the return side of the sump
If I ever want to use the top 40b as a QT tank I can just run an ac70 on it and move the incoming water to the bottom tank which will remove the top tank from the system