Not so much a geek thing, but more a Joe the Plumber thing. I have a PhD in engineering, but I didn't need this to fix the problem. However having this kind of skilz has help me teach engineering for a long time.
I have two rental houses that I own. One was built in 1905 and the other in the 1930's.
Well the oldest one had a plumbing problem with very low flow to both the tub and showerhead in the bathroom furthest from the cold and hot sources. I know this house and I am guessing that the galvanized hard pipe probably dates from the late 40's to the mid-50's so pipe build up might be an issue. If it is that it is an expensive or time consuming fix.
Anyway, the fact that both the tub and the shower flows were impeded and the shower had a bit more flow than the tub made me think that it was an issue with the diverter valve. Visual inspection said that this was probably a Price-Pfister set from the 1970's.
Today I pulled the diverter valve (it was indeed a three handle Price-Pfister set-up) and the seat washer had broken up and clogged everything n the diverter valve. I cleaned it up, went to Lowes and bought a bunch of the correct washers for $2.12 after taxes, and fixed it.
I would have preferred to by a new stem as there was a bit of corrosion on the old stem, but my Lowes did not stock that diverter valve. They did stock the hot/cold valves, though.
Not very geeky, is it.