It is good airmanship to switch tanks each 30 min on the PA28, and WRITE DOWN the time of switch and to which side.
Fuel inbalance should be detected during your 15min FREDAS checks.
The C172 is indeed quite prone to an imbalance due to restricted suction. If you have a situation where one tank is emptying and the other one not, a probable cause is the wrong fuel-cap on the wrong wing. As the Cessna fuel-system is "gravity-feed" based and doesn't posses a pump, the port wing has an excess-fuel drain/pipe. The starboard fuel-cap has a small air-hole in it. This way, no tank wil be vacuüm. change-over the fuel-caps and one will suck vacuüm and therefore not feed.
enjoy the end of the year...
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