Sumps don't stink. Skimmer collection cups do.
Siphon Overflows only drain your tank down to the top of the overflow weir. Usually an inch of water. although this depends on what kind of overflow you have(HOB
, built in, drilled back.)
As long as you determine the max fill line of the sump and don't go above that then it will not overfill during power outage.
Basically after running return pump with some water in sump for a few minutes allowing overflow to reach max flow you turn off return pump. Once overflow is done draining your display you fill sump to the highest level you can without overflowing. Then turn pump back on. Once overflow has reached max flow mark the water level on the sump with tape or perm marker. That will be your absolute max fill line. As water evaporates you fill to that line and don't go over.
Hope that all makes sense.