"Compact" (Mfr Interstate Precision for H. Hughes) vacuum.?

I only have a cloth bag which I clean after every use. Are there paper bags I should be using? Also, the opening at the rear of the cannister - what is it for? I keep it shut at all times, should it be open? (Interstate Precision Products, Model C450/80, Serial #1090668. Would appreciate any info you can supply or get hands on an Manual. Thanks for your help. E-mail = shortcarole@yahoo.com This was my Grandmother's. Purchased I believe in the late 50's from door to door salesman. Works like a champ. Thanks for your help