I am also interested to know. Using the hand get boring and too often my girl is not available.

One thing I have tried is to use the water stream from the shower - that showerheads where you can adjust the stream. That works, but takes some time and concentration. The good thing is - the mess is right away ;-)

I have also tried an electrical shaver - remove the top cover and you will find a nice vibrating thing. Put the whole shaver into a washcloth before using it. Thats the one which works really quick.

Thanks for any further hints ......