Most people want a grill on their deck or patio. Adding a small sink nearby helps with food preparation and reduces trips in and out of the house. Plus, a gas barbecue unit that's built into a tiled countertop gives the cook plenty of convenient cooking and prep space.
Construct the cabinets and countertops to resist weather. Unless you live in a very dry climate, provide an awning or some other shelter from rain so the outdoor kitchen is at least partially protected.
If you have freezing winters, install plumbing that can be drained in the fall. Be sure you can shut off water from inside the house. The drain line shown here runs to a simple dry well and needs no venting. It is acceptable for the graywater that a prep sink produces.
A day to run plumbing and a gas line for a sink and barbecue
Groove-joint pliers, screwdriver, level, shovel, posthole digger, hole saw, tools for joining copper and plastic pipe
Installing PVC drain pipe, installing a sink, running supply lines
Plan the location for your sink and barbecue; build the cabinet
Sink, gas-fired barbecue, supply pipes and fittings, drain pipes and fittings, trap, garbage can, gravel
Dig a hole for a dry well at least 10 feet from the patio or deck (check local codes). Dig a trench to it that slopes down and away from the house. Run the drain line -- 1-1/2-inch PVC probably will be acceptable -- in the trench. Check that it slopes at a rate of at least 1/4 inch per foot.
Punch or drill a grid of holes, about 1/2 inch wide, in a garbage can. Set the can in the hole; its top should be 2 inches below grade. Mark where the pipe will enter and cut a hole for the pipe. Set the can back in the ground, install the pipe into the hole, and fill the can with coarse gravel.