what is through trap
In plumbing, a trap is a device which has a shape that uses a bending path to capture water to prevent sewer gases from entering buildings, while allowing waste to pass through. In refinery applications, traps are used to prevent hydrocarbons and other dangerous gases from escaping outside through drains. In domestic applications, traps are typically U, S, Q or J-shaped pipe located below or within a plumbing fixture. An S-shaped trap is also known as an S-bend. It was invented by Alexander Cumm