Very low yields of plasmid - this is usually attributed to a loosely fitting filter in the column. Check whether the filter in the column is fitted lightly. Check the plasmid copy number. This usually arises from white gelatinous matter remaining above the diatomaceous earth when preparing the solution. Check the diatomaceous earth solution.
Syringes tend to stick and give bursts of vacuum.
If the supernatant in step 5 contains cell debris in suspension because of careless transfer, the column will clog. In this case do not discard sample, but scratch column surface slightly with pipette tip to unclog column. Home made filter columns can be made using microcentrifuge tubes as described by Hansen et al. In principle it should be possible to scale this up to a macro-prep. We have only worked with 20 ml cultures per prep.