Question

I can see messages in poison queue but they get purged after some time. I am not sure how this is happening.

How can I keep them in poison queue and then manually delete them?

This is my netMsmqBinding in WCF service:

<-netMsmqBinding
        <-binding name="MsmqBindingNonTransactionalNoSecurity"  exactlyOnce="true" maxReceivedMessageSize="2147483647"
                 closeTimeout="00:10:00" openTimeout="00:10:00" receiveTimeout="00:10:00" sendTimeout="00:10:00"
                 receiveRetryCount="5"
                 maxRetryCycles="1"
                 retryCycleDelay="00:00:20"
                 receiveErrorHandling="Move">
          <-readerQuotas maxStringContentLength="2147483647" maxArrayLength="2147483647" maxNameTableCharCount="2147483647" />
          <-security mode="None"/>
        <-/binding>
      <-/netMsmqBinding>

Answer 1

Look at timeToLive attribute here
Basically, the default is one day and the message will be discarded if it sits in a queue for longer than a day.