Things didn't go as planned and so our poor pond is still waiting.
I had drilled holes for the tubing but they didn't stay attached with just a little bit of silicon, especially because as it turns out the silicon gel doesn't stick to the silicon tubes. We went yesterday and bought tube connectors and installed those instead. The input we didn't seal because the water will simply pour in but we had to seal the output, which was difficult because the pipe is curved and the connecter has flat edges. We eventually melted it on a flame and moulded it to the curve.
Messy but hey it works.
We simply connected the tubing, which holds the connector in place without having to seal it.
Now that the silicon has cured enough to start I filled it up. First I used a mesh bath sponge to keep the perlite in. I got a small one for free with some soap and it's better because it's so small. I pushed it in with a stick and then poured the perlite in with a funnel and made a mess everywhere.
I tested it now by pouring water in the top and it runs out, albeit slowly. Perhaps this is too narrow? The perlite floats so I need another small mesh sponge to keep it in the top.
I will connect it all up later with the pump but right now I really have to get some work done.