When running waste pipes behind kitchen units and exiting through the wall is it ok if the elbow is tight to the wall so one side of the elbow is sat in the hole. My concern is if it starts leaking you would never no. It would just go in the cavity.
ABS can be used outside, but recommendation is it is painted with gloss paint to provide a degree of protection from the UV in sunlight. I've seen more degraded push fit pipework due to sunlight than I have ABS.