Reading this blog on a washing machine installation and software estimation, that the unknown of a PVC wall in a U-bend spigot inlet caused a problem reminds me of when we moved into our house. We had the same issue with the drainage from a sink overflow dripping into the cupboard below. The previous occupants had tried taping over the spigot, and lined the cupboard with waterproof tape too. They had never checked to see if there was a hole where the water should be flowing! Lesson: check your understanding of the system, and make sure that the basics are right before plastering on multiple fixes.