Oil purging

First off, read the various ROTAX maintenance manuals (Operators, Installation, Line, and Major) for guidance at:  https://www.rotax-owner.com/en/support-topmenu/engine-manuals#912-series-engines

The basic guidance is that any time you open up certain portions of the engine's oil system a PURGE may be necessary.  Opening up the oil system has the potential to introduce unwanted air into the oil lines thus interfering with the oil pump's ability to provide (suck/blow) oil flow throughout the engine.

Having said that, I have found that the above guidance is appropriately conservative.  For example, I have an RV-12 (912 ULS) with a mid-mounted oil tank.  I can safely disconnect the oil input and output lines at the top of the tank to clean the oil tank without having to then perform a PURGE -- my actions have introduced no extra air into the oil lines.  Your aircraft's engine installation may be different -- so be careful.

ps -- Don't confuse PURGING with BURPING.  PURGING is a more complicated maintenance procedure that requires an air source, pipe caps, etc. and is required only occasionally.  BURPING is a regular occurance that is used to assist in accurately determining the quantity of oil in the engine.