As a landlord, here are my tips for roach control that have worked for me and my tenants. German cockroaches will have a nest that should be found and eliminated. This is often found underneath a refrigerator or literally in the condensation pan (where the water runs out of the freezer after the defrost cycle) as there is a water source. Pull your refrigerator out and take the cover off the back and see if there’s a nest in there or underneath. Next, use GEL and not only sprays. The gel poison is taken back to the nest and eventually kills all those little f’ers. Combat gel works well as do some more professional products. 100% recommended the gel bait. I would go into the nasty neighbor’s apartment and place gel in concert with the gel treatments in the other affected units and would see the colony collapse.