The manifold they’re referencing is probably closer to the water heater than the sink. More specifically, it’s probably in their basement or garage. It’s unlikely that running hot water from anywhere will clear those lines.

@DarrinBrunner@lemmy.world, if it begins to bother you too much, do what we did at my friend’s house and turn off the dishwasher supply valve and install a splitter at the sink’s hot water supply valve. I’m obviously making numerous assumptions on how close your dishwasher is to the sink and how accessible everything is.