I have been retained as an expert on a half dozen PCCP and DIP force main failure lawsuits and claims from CA to NJ to MO to AL. The main problem is that the researchers do not test the linings at an appropriate pH, which needs to be down to 0.5 for an extended period. In one case, the Protecto 401 did not extend into the bells or spigots far enough and they corroded, in another the 401 was blown out by sewer cleaning jet of water, then corroded to failure (holes in the wall) in one year or so, cement mortar is gone in a few weeks, John Redner, former operations superintendent for LA County Sanitation said in an ASCE committee meeting minutes that any linings that are brushed on, sprayed on, etc last up to 5 years before failure in an H2S environment. Most of the force main failures occur just over the hill where the line goes to gravity flow. See ASCE Manual #69 "Sulfide in Wastewater Collection Systems". AMIDE-cured Coal Tar Epoxy lining is an energy source (i.e.,FOOD) for the sewer bacteria and is good for 3 to 12 years before pipe failure in a sulfide environment. Amazingly, some associations and manufacturers still recommend it for sanitary sewers. Good luck. Use an air release valve at the high points they can clog. DO NOT depend on flow velocity to push air bubble down the line.