This was a touchy subject in the league I commish as well.
But we've added a few rules since than.
It's hard to make rules for GM's not to tank. So you have to hit them with another angle.
In my league we make the bottom 4 GM's pay $100 extra which goes towards the draft party.
GM's were still 'tanking'.
Than we added the draft lottery. Finishing last gets you a 40% chance at first overall. Obviously this didn't stop the 'tanking'.
Just recently, a couple years ago, we added a few more 'tanking' rules.
1) If you have a non-NHL player in your lineup (AHL, KHL, Europe, CHL, NCAA, ECHL, etc) it's $5 a day for everyday you have him in for.
2) At the end of the year we take the median games played and any GM under the median pays $1/game that they are under.
You will never be able to stop tanking, so we decided to hit their wallet instead. Now I say tank away!
We've been collecting fees for two years now and we have $1500 to spend on our 10th year draft party this summer. Not including the $400 that the bottom four will pay.
TANK AWAY!!!
PS) No one really tanks now. It's funny seeing GM's active when one of their players gets demoted to the AHL. They make the switch right away! Actually one of our managers had Ho-Sang in his lineup for three days after he was demoted. He now owes $15 to the league.