wife calls from bathroom 'the water isn't draining out the bath'.....go to investigate, right enough, bath full of her used water, plug out, nowt happening. 
so the waste goes out through the external wall, along a shallow gradient 2 inch or so pipe for 6 feet then joins the main riser/downpipe. presumably frozen solid. grrrr
It is on the north side of the house and temp hasn't been over freezing or any sun on that wall in at least a week, current temp -13.4.
Thankfully we have a seperate shower in ensuite and waste is internal on that one, so not smelly yet !
syphoning bath water into the loo is not very pleasant 
