Problem: In a multi-story apartment building or office building, how do you quantify the degree to which the waste water stacks are clogged up? If a stack is too clogged, you need to do preventative maintenance and flush the stack. If it's more or less ok, you leave it alone (and save money). But you better get this right because otherwise you will have waste water backup into a suite causing thousands of dollars of damage the the tenant.
Solution:
1) Mario is near a toilet close to the top of the stack. Luigi is near the bottom of the stack (standing beside the pipe).
2) Mario calls Luigi on the phone.
3) Mario flushes a tiny RFID chip down the toilet and starts a timer.
4) Luigi uses his smart phone to continuously scan for that RFID.
5) As soon as Luigi picks up the signal, he says "stop"
6) Mario stops the timer and records the time in transit.
7) Repeat for each stack to determine which one is most clogged and in need of a flush.
8) Repeat after flush to measure effectiveness of the flush process
Notes: For best accuracy this is to be done during low-water use period. Random tenants emptying basins or flushing toilets could skew the results. Also, it may be good idea to drop 10 RFIDs at the same time and measure arrival times as an average. This will avoid the possibility that one got stuck along the way by pure bad luck despite the stack being relatively clean. RFIDs are inexpensive enough that this process could be automated with a RFID dispensor at the top of the stack and RFID reader at the bottom. RFID is dispenses on schedule and a graphical report is presented to the building manager on a monthly basis. These RFID tags will be biodegradable - or not. If not, the RFID tags can be used to measure amount of untreated water each city is releasing into the river/ocean and fined accordingly. After all, if a RFID tag didn't get picked up during treatment, the waste water wasn't treated very well at all.-- ixnaum, Jan 13 2016 ...forgot to mention. If this is done with a dedicated smart phone app, each successful RFID detection makes the Super Mario jump sound.-- ixnaum, Jan 13 2016 random, halfbakery