This is the most challenging thing about most IT jobs. I was working "maintenance" (read: janitor that occasionally builds things) at an outlet mall before I fell in to an internship that led to the VoIP/MSP job I've been working for the last decade.
I'm making a lot more money and I never have to clean up bodily fluids, but rarely does this job provide any real end-of-day satisfaction. Maybe once a month I get to work on a project that when complete I can stand back and have something tangible to be proud of.
On the other hand from just a summer of working at the outlet mall there are a half dozen things I worked on that I can see from the highway as I drive by now 12 years later. Even the cleanup work had a clearly defined "task complete" state that anyone could see.
As for the grass being greener, it's important to keep perspective about what the former was. I think your example re: bodily fluids is a pretty good example :)
But, if that's not something you have the space/money for yet, I think that cooking is a nice substitute hobby. There's a lot to learn with tools and technique, and you get the immediate satisfaction of seeing (and tasting!) your finished product.
Just be careful though -- I've injured myself many more times in the kitchen than in the garage.