Freezing pipes.

[harry]

If you think your pipes might freeze, leave a tap dripping. The one furthest from the stop tap.

[charles]

That happened here by accident. The bath waste is now frozen up.

[GB]

DW left the basin dripping. Luckily running the bath tap unfroze the waste, so I didn't have to get up a ladder with a kettle of hot water in a blizzard.

[Onetap]

I did that once. The waste pipe froze, the basin over-flowed and caused a flood.

[GB]

Best to use a bath tap. That takes quite a while to overflow.

[NY]

I had to unblock both the washbasin/bath wastepipe and the kitchen wastepipe this morning at my parents' holiday cottage where we are living at the moment. The bath one runs dead horizontal from where it emerges through the wall to the right-angle join where the pipe then runs vertical - unlike the toilet soil pipe alongside it, there is no gradual fall. The kitchen one is bowed because there is a long length that is only supported at either end. So in both cases there is part of the pipe where water collects and never completely empties.

I tried the kettle trick in both cases, to no avail, so I had to pull the push-fit connections apart and shake the pipes and pour boiling water into one end. Eventually I got the tell-tale gurgle and long lengths of ice cylinders shot out of the end.

When the weather warms up, I'll be doing a bit of work on both of those pipes to prevent it happening again.