Cleaning roof drains

[lamcote]

Finally got round to doing this for the first time. Spent ages poking rubbish out of the bottom drain hole and vacuuming it out using the crevice tool, must have been 20 minutes each side and I couldn't get anything else out at all so really thought it was completely clean.
Then just before I reassembled everything I took the crevice tool off the vacuum, lifted the drain flap up and just pushed the bare end of the flexible vacuum hose against the outlet of the drain and did my best to create an air tight seal to maximise suction into the drain.
I couldn't believe how much more detritus came out, there was no way I would have got this out any other way.
Thought it might be a useful tip?