Sink unblocking on a Sunday afternoon, well if I've had a few beers at lunchtime and I am unable to attend an easy sink unblocking job it can be a bit of a sickener, but if I'm sober enough to drive the van then this has to be one of the easiest and most profitable jobs.
What has usually happened is that all the fat from the clients Sunday roast has solidified in the trap under the sink, it's an easy unblock, maybe a few kettles of boiling water would have unblocked it, but I'm not going to show off and unblock it with the palm of my hand, and neither will I be using a plunger.
If you arrive at a client's house to unblock a sink, pop your plunger in and it's unblocked in 30 seconds you have a very unhappy client, they're going to be paying for an hours work, plus an additional fee for the weekend callout. So it's best to get a bucket of warm soapy water and dismantle the trap and as much PVC waste as is easily demountable and give it a good wash in the soapy water before reassembling, this might take 10-15 minutes but it gives the customer the impression that you have done something that they would have been incapable of doing themselves, which makes it easier for them to hand over the cash for the fix.
When I am disassembling the waste pipe I will often find a wet plunger under the sink indicating that the client has already tried to unblock it but they probably hadn't covered the overflow or the outlet for a second sink whilst operating the plunger which meant that it would be impossible for the plunger to unblock the sink.
If they'd only searched on youtube, "how to unblock a kitchen sink" they could have saved themselves some cash! And even if they had just waited until Monday morning they could have halved the price it cost to get the sink unblocked.