Aquarium plumbing is the part of your system that rarely gets looked at once it is assembled and has water going through it, especially if it consists of PVC. For that reason alone, it can be a potential source of disaster. Since the plumbing isn’t see through, unless you’re using vinyl tubing, it’s easy for things to become lodged in the various fittings or really anywhere along the line. Additionally, small organisms, like sponges, can build up in the lines and slow the flow of water through the system, or further trap other things like algae and other buildup. To prevent this, it’s best to design your system so that a vast majority of the plumbing can be removed for cleaning. Once the hardware is removed, just soak it in vinegar and run a little water through it. That should remove any buildup and keep your system from clogging up and causing a disaster.