Place your straight edge along the center of the length of your work bench.
Draw a line from the center of the straight edge to the edge of your work bench that you would like to have excess fluid drain off of. Funneling all fluids to the same place allows you to set up a bucket to catch the fluid.
Find the center of the line you just drew and mark it. This is the halfway point of the drainage groove and will help guide you in tapering the groove toward the end of the table.
Attach the bit to the router.
Place a shim on each side of the line with the taper dropping towards the edge of the table. This will guide your routers plunging depth to create a smooth taper.
Start your router and plunge it into the work top at the beginning of your line. Be sure that the table of your router is flush on the shims.
Work your router towards the edge of the table while following your line.
Blow away any excess sawdust from the table before using.