I'm replacing some waste pipes and drainage and need to know what is the best way to fit the waste pipes (from washing machine and sink) into the hopper / gully. The hopper I am using looks like this:
It seems there are two ways I can get the waste pipes into the hopper:
1) Through the black plastic top. The solid part (over the shallow end of the hopper) has two circles marked on it. I assume I can drill these out and stick pipes in. The pipework would be visible this way.
2) The side and back inlets (two of which are visible in the picture). Again, I assume I can drill these out and stick pipes in. The pipework would be hidden underground this way, which I would prefer.
Is there any disadvantage with either of these approaches? If I use the underground approach how should I seal the pipes into the hopper? Or am I not supposed to use the underground inlets for this purpose?