Hi all,
I did some further experiments without much success.
At least I could gain some more experience unclogging the nozzle 
When using PLA and PVA (support interface) the part is printed without clogging the nozzle.
The PLA above some of the support interfaces looks ugly.
So I still need to fine tune PVA printing - but I don’t think this should cause troubles while flushing.
I noticed that the temperature when flushing the PVA when switching to PETG is 260C (max temp for PVA is 250). I tried slightly lowering that temp.
No success - nozzle was still clogged.
Does anyone has good experience using PETG with PVA as support interface ?
Could layer height of 0.8 be the problem ?
Could moisture in PVA cause clogging the nozzle ?
I unpacked it bit more than a week ago and also dried it in my oven - afterwards it was in AMS only.
Not sure how long you can use PVA without needing to dry again.
For now I’ll give up trying to use PVA as support for PETG.