It didn't work.
I got home last night to find the bally thing was still leaking when the overflow was in use, indicating that the bottom seal was bad.
For those who have never seen one of these things, a sink wastepipe assembly constists of the flange (the shiny ring which you see round the plug-hole when you clean your teeth), the pipe which screws into the flange and connects it to the U-Bend, and a nut with a rubber seal that screws up the threaded portion of the wastepipe from the underside of the sink and pulls the flange down to seal it against the sink. It also provides an important sealing function itself, because the overflow of your average sink opens about an inch below the level of the flange into the side of the fitting into which the wastepipe goes. The wastepipe has two large holes in it so that water draining into the overflow can pass through the holes and go where it's supposed to. This water is prevented from dripping out by the bottom seal.
Unfortunately, it proved impossible to tighten the nut and seal enough to stop the leaks, and anyway, I had announced that if it didn't work I was replacing the unit with a silicone-free metal and rubber seal affair I'd seen (but not bought) at Arse Hardware that morning. I had missed my train and used the time thus gained until the next one deigned to show up to go and get more flange bolts for the toilet (I had lost the nuts from the original set I bought at Christmas of course). I returned that evening, just as they were closing, to buy the wax ring I would need. I waited to get that because it occured to me that leaving a wax ring in my car trunk would cause the weather to attain record heat highs and leave me a pool of wax on my trunk carpet. Each time I looked at a nice all-metal wastepipe and flange arrangement they had on the shelves, but it was too pricey to buy on spec.
I heaved a curse or two and unfastened the wastepipe again, to discover that the silicone still hadn't cured after 24 hours! There must be something wrong with it. Either that, or the surface it is in contact with is preventing the curing. I've seen that before, but wasn't expecting it. I'll have to get the metal pipe tomorrow (Tuesday) before I go to work.
It was a matter of only almost an hour to clean off the gluey silicone from the sink. I didn't bother cleaning the plastic wastepipe, since I would be tossing it out. Then I sat on my sofa and watched the last three episodes of Star Trek:Enterprise play to their series finishing conclusion.
It was all very depressing.