We had a Mira Flight shower tray fitted to an en-suite bathroom, and it was okay for about 18 months. Then, the water started to overflow the shower tray while showering because it was not draining away quickly enough.
We regularly cleaned out the channel drain waste chamber body and the waste pipe with special triangular and cone-shaped sponges on sticks to ensure we got into all the nooks and crannies that Mira had designed into the drain assembly’s plastic extrusions.
We also used a drain cleaning coil with a brush on the end to ensure the waste pipe was clear. The drain cleaning coil meant that we could get into the main waste pipeline to make sure the entire route was clear of all blockages.
To prove that there was no blockage in the waste pipe, we tested a sink further upstream, draining away with no problems.
When we removed the channel drain cover and removed the waste tube insert, the water drained away quickly. Putting the waste tube insert back in would slow the flow of the water right down, so we could only draw one conclusion. That conclusion had to be that the channel drain waste tube insert had somehow expanded over time, pressing against the channel drain chamber wall and inhibiting the flow of water from the shower tray.
As unlikely as it may seem, the solution was to cut some of the length of the waste tube and drill some holes in it to facilitate the water draining away at a better rate. This seemed to make a lot of difference, and the water now drains away with much greater vigour.
A more drastic solution might be to ditch the waste tube insert all together, but this seemed to be too severe a solution as Mira included the waste tube for a reason, which was probably to catch any detritus that may make it through the cover. Still, in our case, it was also stopping the water which defeats the object!
I have exactly the same problem with the waste insert on my mira flight shower tray. I’d thought of cutting the insert down to see if it let more water drain away. I didn’t think of drilling holes in it. I assumed the reason for the insert was to stop the smell of the drain? Have you noticed that at all? The water drains fine without the insert in place, but we can then smell the drain