I headcanon once wwx and lwj settle into utter domesticity wwx starts low-key pranking lwj. He once filled lwj's teacup so that it's literally brimming with liquid (see image) and lwj just picked it up without looking and drank the tea. Lwj spilled zero drops. Wwx realized lwj didn't spill because lwj's hand is that steady and lwj's cultivation is that high. Wwx loved lwj more for it. So wwx continues to overfill the tea cups to admire his man's skills.
One day he realizes he could overfill everything: soup bowls, buckets of bath water, teapots. So wwx does. And lwj knows exactly what wwx is doing but indulges him. Wwx especially loves overfilling bath water buckets because those are heavy and watching lwj use his arms makes wwx weak in the knees.
Unfortunately, wwx also gives zero fucks about anyone else and he makes it a habit of overfilling everyone's vessels. Soon, drinking tea handed over by senior Wei without spilling becomes a rite of passage for Cloud Recesses disciples: until your cultivation is strong enough such that you spill no drops while you're focusing on the cup, you can't go on night hunts.
Lsz pass the first try. Ljy missed the first night hunt after the rule was passed because he was laughing too hard at everyone else struggling.