Everyone has their own definition of what "THE Sponge" is. Here's mine, along with some thoughts I'm hoping you or someone you know can benefit from.
Empaths are sponges. When the energy comes floating, wafting, or crashing in... they feel it. It's how they handle the energy that defines how well they handle their gift.
For Newbie Empaths, they can easily become THE sponges (who too often get left by the side of the sink). Everyone talks to them and uses them to clean off their metaphorical dishes. Empaths: these are the folks you love but honestly you don't feel energized after your time with them. They unload the excess energy and you (the Newbie) gets soaked and put back on the sink till needed again. Friends: make sure you love on your Newbie Empath. Help them recognize and respect their gift.
For Next Level Empaths, your days of being on the side of the sink are over. You have either fully embraced being an empath and the positive and negatives of having another developing sense OR you given up the sponge gig.
While you may "feel" a lot and you may "sense" a lot... you let the energy move by you and sometimes through you. You might need to deal with the emotional residue, but you don't invest any of your time or energy beyond that.
Now... for the Veteran Empaths, you've worked your gift. You have taken the road less traveled. You have learned how to make your empathic abilities your friend rather than your nemesis. You've learned to make your abilities only visible to those whose energy aligns. You respect the edge that your gift gives you. You have learned how to mine the value of the empathic energy that comes through (whether it be emotional, spiritual, mental, physical) and use it to be of service to all.
When you think about whether or not you are an empath... take time to think about how you view your gift. I know that I do.