High-density polyethylene manhole inserts from Parson Environmental Products can help eliminate surface water inflow along with unwanted hydrogen sulfide odors and are easy to use and maintain. They include a vented PVC canister that stores 20 pounds of either activated or catalytic carbon. The result is a product that traps and stores all of the unpleasant hydrogen sulfide and methyl mercaptan odor molecules before they are released into the atmosphere. The only item that needs to be replaced periodically is the 20 pounds of carbon since it serves as the absorbent media that traps the odor molecules. One person can easily accomplish this. 800-356-9023; www.parsonenvironmental.com.