I did try using 2 durso configuration at the back, but found it was too noisy so I changed to one, BUT the other one where you have the L shape pipe pointing down, I have this pointing up, which means IF the main durso pipe gets blocked, the second one will be like a drain pipe! Had tested it out and it works really well and you have piece of mind too! :lol:
If you have a look at the first picture of the main tank, you can just see the configuration.