Also vent should be vented higher than the loop. If vent is vented higher than loop, then vented loop is more reliable without duckbill valve. Sometimes water will still drip from vent if discharge lines are temporarily clogged. A duckbill valve is recommended for these loops. A. See RWS instructions manual for more detail.
Adapters are available to reduce the fittings to other standard size plumbing fittings.