We have a kitchen sink with disposer and dishwasher all draining through the same 1.5 inch line. The line runs about 40 feet straight to where it enters the sewer main. The line was installed about 15 years ago and over the years we have had a few clogs that were easily rodded out. The past two years the drain has clogged with greater frequency, about every 6 months and the last time only 2 months since the drain was snaked. Each time we snake it has been the entire length of the run. Why would the time been roddings be decreasing? Is it simply time to replace the old waste line? Should we upgrade it to 2 inch pipe if we do? Thanks.