I am getting ready to install my new battery backup sump pump. The manual(and most tutorials I have seen on Youtube) have the back up PVC pipe connect to the primary pipe after a check valve is installed on both lines. I was shopping for the supplies to install and the display at a big box home improvement store had the 2 pipes connect down in the pit BEFORE the existing check valve, taking away the need for a 2nd check valve. The employee insisted this method works because only 1 will be working at a time. Plus it seems cleaner and easier for me to do. I am having second thoughts after searching for anyone to confirm this method and not having any luck. Any advice is much appreciated. Thank you!