Need to replace the T-stat on my 96 1.8 (ADR) A4 so I thought it would be
worth flushing the cooling system while I'm at it. What's the best way to
flush out the heater matrix? If I start the car and crank up the heat & then
turn it off will the valve stay open so I can just stick a hose onto the
inlet stub? Its got climate control on it (Red digital display with buttons
to alter all the various heater/aircon settings).

The thing has Green (G11?) Antifreeze in it at the moment & I got G12+ from
the dealer which is all they sell now and can (alledgedly) safely be mixed
with G11 - but I think I'd rather just get all the old coolant out
altogether.

I.