Stop the bike dying in winter

[unfazed]

Is there a nice way to drain the carbs without removing them? The drain bolts on my carbs are completely seized

Unfortunately not, remove the float bowls (Carbs off again) Using a lefthand drill bit and drill into the centre of the drain bolt  about 5 to 10 mm. If the screw does not turn, stop drilling. Use a hack saw to cut a slot in the head of the screw and try with a flat blade screwdriver. The heat from drilling should have helped loosen the corrosion. Usual works for me. Drilling first is easier to center the drill on the bolt head than if you shear it. Good luck