Hey Lucky,
According to the AIM, the standard way of departing the pattern is on a straight-out or a 45-degree departure (yet this is not mandatory). It is usually recommended that if you are going to make a non-standard turn (i.e. turn in the opposite direction to the traffic pattern) you wait until you are at TPA + 500ft.
Regulation wise (Part 91), you are only required to follow the marked traffic pattern when approaching to land at a Class G airport (91.126b).
In any case just announce your intentions on the CTAF to get a clear view of what's happening in the vicinity of the airport although remember that not all aircraft may be monitoring it.
In my opinion, a downwind departure from a non-towered airport is something you must do exercising extreme caution. The downwind leg is the standard entry point to the traffic pattern and traffic will be flying perpendicular to it to join. For instance, in the case of Oceano (say landing 29) traffic coming from the NE will usually fly perpendicular to the runway, overhead the airport at TPA + 500 ft to then join the 45 degree entry for the left downwind. If you are doing a right downwind departure from runway 29, chances are you may conflict with arrival traffic that will be approaching from the NE to overfly the airport.
Also check out this AOPA article relating to non-towered ops
https://www.aopa.org/-/media/files/aopa ... s/sa08.pdf
Hope this helps!
-Norberto
