If I'm freezing live clams, purge before or after freezing?
Here provides 2 methods to preserve clams:  


If you will cook these clams within future 7 days, you could just refrigerate them, just put whole package in the refrigerator, and do purging before cooking. Put clams in 2~3% salty water about 2 hours for purging.  
If you need longer preservation, you could freeze them, but remember to do purging before putting them in freezer. Clams will be no longer alive after freeze and unfreeze, and purging will become failed.  


It's the experience from me and my friends who love culinary, hope it helps :P  

Note:
If your clams are vacuum-packaged, both refrigerating and freezing should be OK (Prefer refrigerating, closer to clams living temperature).
No matter what method preservation, cook and eat these fresh ingredients ASAP always better.