Need to have TCP/IP HL7 Inbound service/adapter just write to file - no persistence anywhere in the engine

You could have a 0 day Ens.Util.Purge task running every 5 mins and clearing the production messages. That way you could use only built-in components such as the hl7 tcp service and hl7 file operation

Apologies if too late but I tried the following based on the Non Persistence option used in the EnsLib.HTTP/REST/SOAP Generic classes (also see  Accelerate Ensemble)

1. Custom TCP Service Extends EnsLib.HL7.Service.TCPService:

Class Community.NonPersistService Extends EnsLib.HL7.Service.TCPService
{

Parameter SETTINGS = "PersistInProcData:Additional";

/// Persist data to operations with invocation InProc<br/>
/// The default is On. <br/>
/// This setting is only used if calling an operation with invocation InProc. <br/>
/// If this setting is off then no message headers will be created and message bodies will not be saved.<br/>
/// If this setting is off there will be no trace in the message viewer. <br/>
/// If this setting is off there will be no retry attempts by the operation - only one attempt will be made. <br/> 
Property PersistInProcData As %Boolean [ InitialExpression = 1 ];

Method OnInit() As %Status
{
    Set $$$EnsInProcPersist=..PersistInProcData
    Quit ##super()
}

}

2. Custom HL7 File Operation invoked InProc that is the target of the service

Class Community.InProcOperation Extends EnsLib.HL7.Operation.FileOperation
{

Parameter INVOCATION = "InProc";

}

Note the property description from EnsLib.HTTP.GenericService for PersistInProcData states for synchronous sends but this needs to be removed since not relevant for InProc. Sufficient that InProc target processed via OnMessage.