yeh Vribb bunnings or clark rubber its great in low pressure/low flow low angle but under load flat or flaky/prickly gold lifts out i'm afraid.
It works best with 2mm expanded mesh floating about 1.5 above it in a sluice.
This isn;t some blind statement i did extensive testing a few years back with 15 grams of varied gold it's really great for crushed gold and 100, 200 mesh but after that you either hold too much white sand to be effective or you cast your gold out from pressure. also this rubber has a tendency to hold air creating little trampolines for your gold to get stuck to whihc floats right out.
Sorry smoky bandit reason you only see the gold at the start is most likely because water gains momentum and carries gold off, there's a bit of a myth about
"i catch all the gold at the top so i'm not losing any" reality is gold will drop out at different times under different pressure and it will separate from clay and dirt or quartz at different point in the sluice so expect to see a bit of gold through your system if its working well.
On the subject running a test pan at the end of your sluice is not a good way to test losses either the only real way to test losses is to dig a hole and highbank into it, the pressure creates a vacuum and you cna test pan after a session and should always see a few flakes or you didn;t feed enough