
Originally Posted by
SephYuyX
It's most likely just a lot of build up at where it goes in to your septic, or worse there could be a crack there and roots are getting it.
Call your local plumbing company (ACE for example) and ask them to have them clean out your pipes with their high pressure water jet and reverse flow nozzle. If you have these yourself, you can do it, but it's just simplier to have them do it. It will cost about 100$ roughly.
If this works, but it happens again months down the road, you mostly likely have a cracked pipe, in which case you can get them to bring a camera in to see what the problem is.