Hi Doug, A french drain would be perfect for what you are doing. You can but premade plastic collection basins at any Home Depot or Lowes that will serve as your primary collection area. It is made to accomodate standard PVC piping that you will run from the sink drain. Obviously, you will have to place this into the ground. Dig a hole 2-3 times the size of the basin(depending on the porosity of your soil) and place some gravel in the bottom of the hole, at least 6 inches. Place the basin in the hole and add 3/4" coarse gravel around basin. The basin has weep holes that will allow the water to drain into surrounding gravel. Make pvc pipe connections and don't forget to add a vent so the sink will drain properly. The vent can terminate into the shed, if you like, but I'd run it through the roof, just like your home, to keep fumes from entering the shed. Also, be sure to add a P-trap under the sink to keep fumes and bugs from coming back up into the shed through the drain. Be sure not to wash chemical fertilizers and pesticides down the drain, to keep the groundwater from being contaminated. Take a visit to the hardware store to see the available parts and you should be able to figure it out. Good Luck.