Flooding the tunnels was a prospect I suggested early on. A few miles of hose and a few bigaxx pumps should make them un-usable in short order. It should also make the connections way more obvious since tunnels are usually dug on a grade line and the water would come out someplace. Besides wiping out the tunnels a salt water wash down should also destroy all the goodies the hamassholes have stashed in them. And there shouldn’t be any extra harm to any hostages the muzzards are keeping in them. They’ll all come out doing the backstroke in the rising water.
Egyptian military in the recent past used raw sewage to flood smuggling tunnels connecting Sinai and Gaza. Yikes.