The trap, in a the context of plumbing, serves to prohibit undesirable sewage gasses from entering homes and buildings.
This is done by 'trapping' water in the bent portion, thereby stopping gasses from passing through.
I'll admit it: I LOVE traps.
While not the product of emotion, intrigue, or desire, the simplicity and essential nature of the trap design warrants it a spot among the great designs of all time.
Not only is it essential in function, enabling home sewage and waste disposal safely, but it fulfills its mission in the in the most 'essential' way possible, with no moving parts, nearly no maintenance or points of failure.
Additionally, the is no obfuscation of its method. From the first glance, it is clear what it does and how it does it, it maintains a now rare level of 'obvious-ness', providing satisfaction in its assurance of form and utility.
While certainly not 'pretty', I think there is a strong argument that in its pure, unassuming, perfect existence, beauty can still be found.
The purity of intent and purposful elegance is absolutely inspiring. It reminds me of the saying 'I'm sorry for the long letter, I did not have time to make it shorter.' The skill and attention to detail required to reduce an object to its most basic and genuine essentials is hard won, and this is the perfect motivator for the development of that ability.