Bottom cap on fuel filter assembly 743/843, drain plug?

What's supposed to be on the bottom of the fuel filter assembly? On mine, something seems broken off and there's a small constant drip. Is it a plug, a valve, and when is it used? Is it used for draining water, or is it to drain fuel when changing the filter? I don't want to take the unit apart until I have everything I need lined up to put it back together again. I do have a new filter cartridge ready. If you know the specs on the bottom thing (e.g., thread size), maybe I can get a generic one. Thanks fo rany advice.

There is a drain on the bottom to remove water. The filter acts as a water seperator.

Wish it was a water separator. The stock Bobcat filter on older machines doesn't separate water. It just drains out fuel. It needs a plastic element/baffle in the glass bowl to separate water. Look at this picture, or others, mostly from diesel boats, for the water separator element in the filter. Just another reason to switch to the spin-on filters that incorporate a water separator inside them.
http://www.google.ca/imgres?q=lucas+diesel+water+separator&um=1&hl=en&biw=1276&bih=620&tbm=isch&tbnid=TY1_HF7x21W2NM:&imgrefurl=http://www.dieselnet.com/tech/diesel_fi_comp.php&docid=maNWP7OdyAa1BM&imgurl=http://www.dieselnet.com/tech/images/diesel/fi/comp/~4-12.gif&w=261&h=350&ei=y2ZiUPqfPISC8QSfqoDwAw&zoom=1&iact=hc&vpx=206&vpy=226&dur=424&hovh=234&hovw=175&tx=115&ty=135&sig=101663290456137751586&page=1&tbnh=135&tbnw=101&start=0&ndsp=20&ved=1t:429,r:14,s:0,i:112
...karl