Hi! I was wondering what happens during susukudo?

I believe you're referring to Sansankudo (三々九度) . Meaning " Three By Three (Nine) Exchange ," it's the ritual exchange of sake cups that binds a geiko and maiko in an onesan/imōto relationship. A set of small cups, followed by medium cups, and then large cups containing a small amount of sake are drank by each participant. This completes the ritual and they are bound in sisterhood ^^