Plumbing Parts Explained Bulkheads - Use bulkheads to connect piping through the side of an aquarium or sump. Locklines - Use different sizes or shapes of locklines to control and direct current in your aquarium. MTP Fittings - Use MTP fittings to connect pvc pipe and clear tubing. MTP fittings are also called adapters. Clear Tubing - Clear tubing is used for all sorts of aquarium plumbing applications. Use it to connect return pumps to the aquarium, and to connect U.V. sterilizers, chillers, etc. Drain Hose - Use to connect the drain of an aquarium to the sump. Clamps - Use to clamp clear tubing to fittings. Check Valves - Use a check valve on each return line to prevent excess water from siphoning out of your aquarium if the power should shut off. Check valves allow water to flow freely in one direction, but have a flap that closes to prevent water from flowing backwards. Ball Valves - Ball valves allow you to easily adjust the flow of water through the pipe and to shut off pipes when needed to make maintenance easier.