In a nutshell tanking means to deliberately avoid levelling up by finishing below 8th place. That way your squad do not lose 20% condition for the following season. There are many threads about this and many pros and cons. I’m surprised an experienced player such as yourself has not heard of this though. At level 55 you’re most likely at or near the top of your server so tanking for you would be difficult due to a lack of active teams at that level. You may find that everyone levels up in your league.