We just found out that our home has a Josam Backwater Valve installed in our basment and we've been living here for 5 years. House was built in 1954. I like to know if i can replace the swing check valve assembly that has been in the valve body maybe for 15-20 years. How much should it cost if i were to hire a plumber? Manufacturer says swing check valve assembly is treaded to the 4' pipe.