That's what I was thinking. I personally don't have experience with newts, but the hip protrusion led me to believe the newt was underweight.
It's the same thing with goldfish kept in bowls. They may seem to live a long time, but quality of life is minimal. Finding a 20 gallon tank is not that expensive, nor difficult. At the very least you should find a non-toxic plastic tote box that can hold that amount of water to give it a better habitat.
I didn't want to sound too harsh, but I agree that the newt needs far better care to thrive. If you feel what you've been doing is fine (since it has lived this long), even a dog can live 10-15 years kept outside in a shabby dog house and fed cheap food. That doesn't mean it's happy, or well. It's just squeaking by.
Amphibians are resilient creatures that can survive long, harsh conditions, but I agree it's quite remarkable and a bit sad that yours has lived this long with such inadequate conditions. Give that thing some nice squirmy worms, improve it's living conditions and it could stay with you for a long time.
Just doing the bare minimum for an animal, whether it's cute and fuzzy or small and slick, amounts to neglect. Education to pet owners like yourself isn't often widely available from most pet sources. I'm very happy that you posted here and you seem to want to give your newt a better life. Please keep in touch and we will be happy to guide you through giving this guy a great second half of his life.