Where on Earth does it all come from!

[HPsauce]

Interesting. I took the nearside drain out - easier to get at and as my drive has a slight slope it's the "downhill" one.
A good 700ml of slightly-coloured water came out of the condenser tray.

I then took the orange drain pipe indoors to inspect. It looked ok at first glance, but was definitely blocked.
The exit tip was clear, I'd trimmed it back a bit previously so the slots were open about 3mm anyway. I think the blockage was in the "horizontal" pipe section, it blew out very easily.

I collected the bits. It was plant debris, all quite small only 1mm or 2mm along/across. About half was unidentifiable black woody/seedy material and the rest was those blasted seeds!

It obviously settles in the tubes as water dribbles through and slowly builds up until blocked. I can't think of any obvious way to stop that so I guess it will just have to be a regular maintenance job.

Still need to work out how the excess water/debris arrives there though.