When I went to UK it still felt like mid winter so I was worried about things freezing. A friend in Bulgaria has a hostel and campsite there and has had several toilets destroyed by ice damage. I therefore thought it would be worthwhile pumping out mine with the wet & dry Hoover to avoid this risk. Now I'm back home and the whole house stinks of sewage! This was clearly not the right way to winterise a toilet but what should I have done? Should I have added salt or something to the water?

Should I have added salt or something to the water?
Yes
And drain down the water systems, empty the hot water cylinder and put the right type of antifreeze in the CH.

Protect Toilets: Flush toilet and hold handle down for 30 seconds after flush to help empty tank. Sponge out all remaining water in tank. Dip or sponge out water in toilet bowl until 2-1/2 to 3” remain in bowl. This will prevent sewer gas from escaping into your house. This gas is not harmful; it just smells bad. Pour one cup of permanent antifreeze into the toilet bowl and stir it around briefly. Pour one cup of permanent antifreeze down the over flow/refill tube in the tank. This tube is about ¾ inch in diameter and extends from the bottom of the tank to just above the tank water level. You should see some antifreeze run out under the rim of the toilet bowl.

From this guide

Useful links Rural, thanks.

You're welcome. I was surprised when reading it as there were things I hadn't even thought of!

I'm just designing my plumbing system at the moment so it was useful to have this article on winterising to bear a few things in mind when laying out the pipework, like having all the pipes sloping down towards the lowest point and fitting a drainage tap there, as well as drainage taps for the boiler, expansion tank and pump housing. One of my friends had already mentioned getting a cheap compressor to blow the system through to ensure there are no water pockets trapped in the pipes. I hadn't thought about leaving water in the U-bend with anti-freeze in it though, and probably would've emptied it completely and ended up with a stinky bathroom like fidobsa!