3" x 3" flexible pipe coupling  
3" x 3" flexible pipe coupling  
     
     
3" x 4" flexible pipe coupling  
3" x 4" flexible pipe coupling  
     
3" x 6" flexible pipe coupling  
     
4" x 4" flexible pipe coupling

Flexible PVC (provides a good vibration dampener for reducing noise)

 
4" x 4" flexible pipe coupling  
4" x 6" flexible pipe coupling