The Dranjer seals the sump basin while providing a valve for water to pass down into it. Normally, sump basin lids are completely sealed. This is good in that it prevents water and foul odors exiting the sump pump, but the drawback is that if there is ever a flood event where water covers the sump pump, there's no way for water to get into the sump pump from the lid. The dranjer lets water fall through the lid into the sump pump if ever needed.
