In this kind of test, a penetrant liquid is used on a surface (in this case a weld area, 溶接部) to check if it has defects.
Here I read that 水洗式 refers to a flush toilet, but in this context it doesn't make much sense to me. Could it refer to a drainage outlet or something similar? I mean something used during the test to collect the dripping of penetrant liquid?
Thank you for your help!