How will you remove mercury from the well?
Read the rules, please, before suggesting such kind of things. By rules you can't leave materials in the well (as you've already guessed), you can't create pressure in the well (or it will be too easy) and you can use pipe but if you won't I'll give extra points.
There are 4 days till the end of the contest, so I'd like to post a temporary participant table:
You still can take part in this contest, and you can improve your creation also, so there are chances that somebody will share the first place with Fast-Driver :-P
Water remains in the well, but it must be empty.