Thicker products should have larger drains. They just don't work otherwise (not that this matters to some as long as they can check the box they don't care). Material can be the same as the surface sheeting, most likely aluminum - no real benefit to having the sheeting corrode away but have the drains not. Drains have to dip into the liquid 102mm - check your length and mounting elevation. Also, drains need to be in every isolated area which can be quite numerous. Drains with balls or floats won't work with heavy liquids or waxy liquids. Drains are often not where the low point is - liquid gets on top, the weight depresses the deck making a low point and if you are lucky there is a drain there. Otherwise it was a waste of emissions. Better is to use engineering or management controls to eliminate the possibility of liquid being on top. My opinions only of course...
