Water seal controls
Water seal controls means a seal pot, p-leg trap, or other type of trap filled with water (e.g, flooded sewers that maintain water levels adequate to prevent air flow through the system) that creates a water barrier between the sewer line and the atmosphere. The water level of the seal must be maintained in the vertical leg of a drain in order to be considered a water seal.
40 CFR § 63.111
All terms used in this subpart shall have the meaning given them in the Act, in subpart F of this part, and in this section, as follows.