I'm new at DIY plumbing, so appreciate the advice.
I've been making some additions in my home and I've had to learn how to sweat and join water pipes. The first few looked like bird droppings, but as i learned to get the right temp, the sodder just runs right in...
After all the joins are done, one of the hold-your-breath moments is when you turn the water on... So i think i've been lucky and haven't had an immediate leak, but my question is this - if there is no immediate leak, does this mean I have a long term hold..? I'm assuming that with the water pressure if it doesn't leak immediately, it never should... is this correct or am i wishfully dreaming..?
If so, how does one make sure the sodder was 100%?
Usually, if it doesn't leak when you turn on the normal water pressure, it won't leak. It could last for many, many years if done right, or it could eventually leak if poorly done. Heat the fittings, not the pipe. The biggest mistake that new "solderers" do is to overheat. Don't be afraid to back off with the torch as soon as the solder is pulled into the fitting.
If any of these connections are permanently exposed and accessible, such as under a sink or in a utility room or closet where they will never be enclosed, you can use sharkbites or compression fittings (no soldering).