You heard correctly. Rotax calls out on the 912 ULS for the oil bottle to be cleaned every 200 hours. The procedure is called out in the 912 line maintenance manual, Chapter 12-20-00 section 11.5.
This process is a little more difficult on the S-7S because you cannot remove the bottle from the firewall because it is encased by the engine mount. The task can still be accomplished, you just have to do all the steps with the bottle in its mount.
You are welcome! The process is fairly simple. I like to disconnect the oil lines and cap them to keep contamination out of the system. Remove the tank cap and filter assembly and set aside to clean. Wipe all the oil sludge from the can. Make sure the oil bottle is reassembled properly and then purge the oil system. The reference for purging the oil system is directly after the oil bottle cleaning section in the Rotax line maintenance manual.
Feel free to ask any more questions as they arise.