At this point, a top school like Sinai will assume that everyone is still interested - those who have "better" acceptances should certainly already have let Sinai know that they wish to come off the WL.
Some schools may ask WL students to send a letter of continued interest or remind the students to tell them when they decide not to stay on a WL- but that will be closer to May 1. By May 1, schools will have a better idea of how many students they need to accept off the WL and that is when the big WL movement will happen.
There are some Top schools, including many in same geographic region, with non-rolling admissions who will be sending out acceptances this week and next, and some of the accepted Sinai and WL Sinai students will be getting offers from these other top schools. I think that will impact Sinai's numbers. But to answer your question, you do not need to do anything now, and take your cues from any direct information that Sinai sends out to you as someone on their WL.