SAFETY 1ST: As with any odor you are unsure of, take appropriate measures to insure your safety in case of propane or gas leaks. Once you have eliminated the possibility of a propane or gas leak, you should have the septic system pumped if it has not been done recently. If odor is still a problem, check for a broken or leaking line coming from your house to your septic tank. Breakage and leaks most often occur with older lines made from materials such as steel or cast iron pipe. Breakage is most often caused by freezing and thawing, wet to dry conditions or settling of ground. Doing a dye test can be useful in determining if you have a broken or leaking line.(*Be sure to use dye made especially for use with plumbing fixtures and be careful not to overflow a lower drain or toilet when doing a dye test.) Introduce the dye with a substantial amount of water down the toilet or bathtub, then check your sump basin for signs of the dye. It may be necessary to plug the line at the septic tank in order to build pressure on the line. If you determine that the line is broken, it must be dug up and replaced with PVC line. Be sure to replace the entire line, being certain the new line runs through the basement wall and through the wall of the septic tank. Replacing only the bad section of line would only set you up for further problems. Odor from your sump pump could also indicate a high water condition with your septic tank. You may have water from the leach field and septic tank escaping and seeping up through the stone around the sewer pipe causing it to back up into the sump pump. One option to help with this situation may be to buy around six bags of sodium bentonite to mix with the ground around the sewer pipe. Sodium bentonite expands when wet and can potentially absorb several times its dry mass in water. This will basically plug off the water. You can usually purchase sodium bentonite from a feed dealer for around $7.00 a bag. Ask your service provider for further information on how to deal with a high water condition.