Sink Drain Pipe Size Code

Bathroom vanity with cooper sink.

Sink drain pipe size code.

The last size is 4 inch drain pipe that can be connected to 160 units in horizontal stack and 240 units in vertical stack. All the pipes that connect to the tailpiece including the p trap assembly. Some older sinks may have drains that connect to a 1 1 4 inch tailpiece but most modern drains have a 1 1 2 inch outlet. To be safe install more supports than are required.

Horizontal drain pipes connecting the sink drains to the trap must have a minimum slope of 1 4 inch per foot toward the trap. Tables of plumbing drain pipe vent pipe sizes critical distances to plumbing fixtures. The horizontal pipes connect to the trap with a double wye tee which has two y shaped inlets and one outlet. This is the minimum size to use for building sewer or drain pipe that is connected to the toilet.

This pipe size is commonly used for sanitary drainage. You ll see these distances also in our sketch at left. A single trap can service more than one sink but adjacent drains cannot be farther apart than 30 inches. For instance the minimum pipe diameter for a washing machine drain is pipe with a 1 1 2 inch diameter.