I am trying to rebuild three pieces that connect to the filter, pump, and multi-port valve for my in ground pool. Instead of using rigid PVC like the original pieces do I am going to use Flex-PVC. When I bought the new fittings the store gave me a piece of 1.5" Flex-PVC to use but this is hard to fit into the new fittings. No matter how hard I push I cannot get it to the bottom of the fitting, the lip. Should I get 1.25" Flex-PVC instead?