Walmart offers the Instant Power Septic Shock 2-Liter Bottle for $4.28. Opt for in-store pickup to cut it to $4.10. (Amazon charges the same when you check out via Subscribe & Save.) That's $1 under last week's mention and the lowest price we've seen. (It's the best deal now by $6.) It's designed to break down clogs and restore lateral/leach field lines.