Loving the ingenuity, nice work! I’m keen to see the video of it working. As someone who works with stainless steel every day I appreciate the effort you’ve gone to - it’s not always an easy material to work with.
Two practical observations though. First, how are you going to clean the inside of such long pipe work when it invariably furs with detritus?
Second, the open area for the inlet pipe looks very small, particularly as you’ve added the mesh inside. A couple of leaves stuck to it during use, and you may find a significant drop in flow.
If it were me, I’d do away with the slots completely, cut out the entire opening where the slots are formed, resulting in a larger rectangular section of visible mesh for the water to draw through,
thanks for the input, the pipes furring up, I hope being stainless it will minimise that to an extent. even so, they are easily removed from the bar holders, it's just a grub screw on each holder and it slides off. I was thinking either running an outer of a bike brake cable down there with a bit of rag tied to the end and pulling it through or attaching to a drill and letting it flail about in the tube. another thing I thought of was taking them off and running a hose or pressure washer through it. failing that it would be easy enough to take both off and soak them in bleach. being metal tubes they ought to be forgiving to rough handling, unlike glass. the pipes on the inside of the stand will be clear silicone so I should get an indication of the state they're in.
the opening I have to admit is a little bit of a concern. you can't really see it on the photos but the gaps wrap around the majority of the pipe, which ought to be ok if a leaf sucks on there, unless it wraps around the whole pipe. I worked it out that the surface area of the gaps was over double the ID of the tube.
so it seemed fine but once I put the mesh in I did think it might be a bit of an obstruction. I tested by blowing down the pipe with the gaps covered but the end of the tube open then compared blowing down the tube with the end covered and gaps open. there was definitely a difference, so I think ideally I need more gaps in there. I was going to do 12 gaps originally but it took so long I settled with 6. I've thought of a quicker way to do this though and the current tube has some scratches on, so I may well redo it with a new bit of tube and 12 gaps.