A Flexible toilet drain is a type of pipe used by plumbers to extend the pipe&action=edit&redlink=1 "Pipe (material) (not yet drafted)") of the drain trap of a toilet, when due to various circumstances it is necessary to change the location of the outlet of a toilet. It is clean, and in fact the easiest way to move a toilet, or simply change it for another with different measurements or a different placement of the drain hole, although the elbow model to use will depend on the location of the outlet pipe and where you want to locate the new toilet.

Currently, a common application of siphons is in the drains of sanitary appliances (sinks, washbasins, toilets, etc.), to prevent the bad smell of putrefactive materials in the sewer from coming out through the drain hole of the appliances. The most classic model (and the one that works best hydraulically) consists of a tube in the shape of an "S" lying down, so that, when draining the device, the water fills the two branches of the tube, up to the drain level of the second, maintaining a plug of clean water that closes the entry of odors.[1]​.

There are different types of toilet drains for special cases.