But I have a closed sump in the bilge the icebox first drains into. From there, a small Jabsco hand pump easily pulls it out of the sump, and out the T. It would also work this way without the sump in line. Are you sure the galley sink is below WL on one tack? I'm sure my T is below WL at times on the starboard tack, but the drain line then goes amidships where it would always be above. There's no check valve and this set up is as designed and built.