Always have homeowner Warranty. Banks will not provide you with the warranty if it is a REO. You should get one which is about $360 - $400 per year. It covers all appliances, heating system, plumbing etc. The coverage will be different with different company. Check and compare.
I don't understand what your friend meaned to replace the sewage. Sometimes it might be clogging by root getting into the sewage. This might happen in any home. As a homeowner, we have to take care of home annually.
Please let me know if you need more information.