Allow air to enter DWV systems to balance pressure as water drains out of the system; eliminating costly roof penetrations and vent lines. No. 1ATD5 vented up to 500 DFUs on a stack; No. 1ATD6 vents up to 160 DFUs on a branch and up to 24 DFUs in a stack. No. 15W940 has a replaceable cabin filter to reduce odors from the plumbing drainage system.