iRule only runs once

when HTTP_REQUEST {
 Collects the entire payload as per content lenght 
HTTP::collect [HTTP::header Content-Length]
}

when HTTP_REQUEST_DATA 
 Sets var to string 
set string_to_find [findstr [HTTP::payload] TAG  4 <]
log local0. "String $string_to_find identified in Request payload"
 Release payload
HTTP::release
}

when HTTP_RESPONSE {      
 Disable the stream filter by default      
    STREAM::disable       
 You can use strings or Regexs to match string (this one matches email addresses)
STREAM::expression {@[a-z0-9._%+-]+\@[a-z0-9.-]+\.[a-z]{2,6}@@}  
 Reenables the stream filter  
    STREAM::enable    
    }  

    when STREAM_MATCHED {    
 Sets data to replace
set data_to_replace "something"
     Replaces string with var    
STREAM::replace $data_to_replace   
    }