There may be several situations where the filter cone or basket may be overflowing:

• Coffee grind too fine
  Try a coarser grind. If the grind is too fine, the water takes longer to flow thru the grinds, causing the filter basket to overflow.

• Coffee too fresh
  Make sure not to use coffee right after roasting. Let the coffee degas for approximately 3 days. If you brew freshly roasted coffee, the CO2 will form a thick foam (crema) inside the filter causing it to overflow.

•  Paper Filter Collapses
  Make sure you fold over the Melita #4 paper filters along the seal (seamed edge). This way, the paper filter will fit better and prevent it from collapsing when you insert the cone filter basket into the brewer. Alternatively, use a permanent gold tone filter.

• Too much coffee inside the filter
  Make sure you don't fill too much coffee into the filter. When hot water hits the ground coffee inside the filter, a blooming process starts (foaming up), that may cause the filter to overflow.

• Hole in the Filter Basket clogged
  Make sure the hole at the bottom of the Filter Basked is not clogged up.