as per chee's guide: http://www.perth-wrx.com/vb/diy-mechanical-modifications/10390-radiator-coolant-flush.html

"Step 4: Remove the thermostat housing and the thermostat." does this have a gasket? and if so I guess it would be recommended to replace it? can someone just clarify that for me pls, ive just dropped the coolant from the bottom hose connected to the thermostat..seems to have got it all out but yeh..wanna do it right obviously

also, I got this Tectaloy radiator flush..has anyone used this as it says drain..then fill backup with water only and the bottle for every 10litres of water which is 500ml...and run motor for 10mins minimum ...isnt this gonna overheat? maybe?

yes there is a gasket around the thermostat. If your thermostat hasnt been out for many years its probably a good idea to replace it. Only like $3 for a new rubber o-ring gasket.

If you fill it up from cold and idle for 10 mins it probably wont over heat. But keep an eye on it anyway

You want to cycle the flush solution as much as possible so burb and bleed the system of air with the flush solution in it so that it cleans the whole system properly not just the block.

Then drain and re-fill again with fresh coolant.

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