I had time yesterday to do some more fiddling with the Droughtplug Recycling Kit I reviewed on Friday. I had a greater level of success but it was far from unmitigated.
I was working with a bath-full of water, left over from the night before. I was able to put the adjusted plug unit (with extra rubber added to provide a better seal) into place and it did prevent water flowing away down the plug hole. With further experimentation, I did manage to get the syphon running. One discovery was that it is better to gently squeeze the rubber bell rather than compressing it flat; the former establishes a flow while the latter gives a powerful squirt that has to wait for the bell to expand again.
It also helped to string the hose outside the window along a gradual descent rather than straight down. This gives a proportionately greater volume of water flowing downhill under the influence of gravity, which is what is required to continue drawing water out of the bath. If we are going to keep using the device, I will have to see if I can rig up some hosing in a semi-permanent fixture along the side wall of the house to make the most of this.
Therefore, the kit does work after a fashion (albeit at a slow trickle). I think it would be helpful if it was accompanied by a leaflet on the science of syphoning as well as adjusters to make it fit a wider range of plug holes.