Congrats!
Urinal. You need a urinal. No water? No problem.
Behind the shop dig a hole deep enough for two 5 gallon buckets, and slightly larger (a couple inches or so). When you are done with connections bury them 8 inches under the ground- drill holes in them and surround them with rocks. This is your mini septic tank. I attached a 1 1/2 inch piece of PVC pipe through the bucket cover. You don't need to attach the buckets if you have them near each other with holes drilled in both of them with gravel between- the water flows from one to the other.
Through the wall bend/cut/fit a piece of 1" PVC- this is your plumbing. Slide it in the 1 1/2" pvc that runs into the buckets. This is your vent and inlet. Put a trap in it (the bend) so the smell doesn't come back through. Make sure the end inside is a little below urinal height. Attach a 1"-1 1/2" adapter to the end of the PVC. To this you will affix an empty 1 gallon plastic container- like a windshield washer fluid container. You will cut the bottom out of it- that is your urinal.
Pick up a cheap windshield washer pump. Drop one line into a 5 gallon bucket of water, and attach a wire alongside the pipe to the outlet end. Bend the wire/hose so it comes over the top of the plastic container and hits it at an angle so it sprays around the jug without spraying out on to you. Wire a switch for the pump where the handle would be.
So, you step up, use the urinal, flip the switch and allow the water to flush, then flip the switch to off. Two 5 gallon buckets is plenty big for a septic for such a small amount of water production, and should allow easy dissipation, unless your soil has a high water table or is solid clay.
I had this rig in my old garage before I put a real urinal and sink in my current one. It works sweet and doesn't smell at all, unless the trap evaporates out. A windshield washer pump doesn't use much energy at all- rig it to a 110-12v adapter, or run it off a car battery. I just had a marine battery I used, but that was because I have a fishing boat.
If you don't have a urinal and resort to pissing outside it will start to reek, and it's a PIA to run to the house when you are in the middle of something, like say a good beer. Mine worked for probably 10 years until we moved.
Just don't have it inspected.

A link to a drawing:
https://docs.google.com/drawings/d/1wY7hLpRkStWJNZ8V2-EPVl9m4SwEC5pNxwR29uD1p8U/edit?usp=sharing