Question-Water bills and Municipal liens after Sherriff Sale- PA

[Justin Summers]

I purchased a home at a mortgage "Foreclosure"/ Sherriff sale in June in Luzerne county PA. 

At first the local township send me the water and trash bill starting from the date of the sheriff sale.  Then they sent me a letter along with a bill for water and sewer from the prior owner for the last 2 years prior to my purchase. They really don't know one way of the other if they are entitled to back water and sewer charges. 

My question is if the water and sewer companies never filed a recorded lien am I still responsible for the bills 2 years prior to my purchase? I realize if they had filed and recorded a lien I would be responsible but are water and sewer "super priority" in PA were as they don't have to file a lien to survive a mortgage sheriff sale?  

Thanks for any insight.