The easiest way to discharge a battery would simply be to use it on your device whether it's a RC plane quad or surface vehicle. I have even held the aircraft while I discharged the battery. Doesn't work too well for surface vehicles. Using a battery alarm and timer can help with that and for those who have telemetry even better. Lipo's cell voltage wants to be in the neighborhood of 3.8 volts per cell for storage voltage.
Do not store LiPO batteries at full charge. They have a much higher chance of catching fire in that state. At 3.8 volts the battery is less likely to catch fire assuming there's no physical damage or something wrong with it.
The safe way is to use the storage mode on charger.
Problem with using (storage mode) or (discharge mode) on your charger is the charger may not have that fast of a rate of discharge to store or discharge battery taking more time to complete the task and needs to be monitored. Some people have connected other loads to the battery usually with having a battery alarm connected to Battery discharge voltage and alarm sounding to let the person know that it's time to stop. There is a little risk of discharging the battery too much and damaging the battery this way.
Another way to discharge or store the battery by using the battery to begin with as the power source to the charger and charge another battery that was over discharged or needs charging, say a battery that was discharged to 20%. You want to charge it back up to 40 or 50% for storage and the battery will charge quicker the next time around. Minimum Lipo storage voltage should not be more than 3.9 volts per cell. 3.8 or 3.85 is good. 3.7 minimum storage voltage recommended but it's not written in stone. You could get away with 3.6 so long as the battery was not discharged too hard or too low meaning Load voltage is not the same as resting voltage or no load voltage. Also assuming there is no self discharge over extended amount of time.
There is a feature called regenerative mode or (recycle mode) on some chargers not to be confused with (cycling mode) which is something else entirely and not used on lipo and lithium-ion or life batteries. In a sense the charger is doing the same thing as above but it's actually monitoring the battery that is discharging through the balance lead and if set up properly will stop automatically.
There are those who use the light bulb technique which if left on too long can drain it down to zero damaging the battery. Battery alarm might help here as long as it works and is set properly. Better to keep an eye on it as it's discharging. I have even thought of using a voltage detector that would disengage a relay for discharging for storage voltage.
Monitoring all cell voltage would be better. Use a battery alarm connected to balance lead that will trigger a device controlling a relay disconnecting discharge load. This method obviously does not work for charging a low discharge battery to storage voltage.
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