Tezos documentation states:
A small delegate who is afraid they might be deactivated because they were not given the opportunity to create any block or endorsement can ensure they do not become deactivated by making small, meaningless transactions with their security deposits once every two cycles.
I wonder what exactly is a "small, meaningless" transaction. Is it the lowest possible allowed by the wallet/client? Also, what type of transaction is this? Can be both adding and subtracting funds from the deposit?