Problem: I’ve just put a brew on using some cheap equipment from an online retailer. The lid of the fermenting bin is loose fitting so the beer is gassing around the lid or through the airlock grommet and not through the airlock / bubbler itself. This is not really a problem while the Krausen is building and lots of gas is being produced, but can be a problem when things slow down, and air gets in.
Lid Fix: The loose lid can be fixed by liberally applying Petroleum Jelly around the lid. Vaseline the company make Petroleum jelly readily available in chemists and supermarkets, and it’s commonly used on babies apparently for some reason or other (no idea).
Baggy Grommet Fix: Place some PVC tape around the bottom tube of the airlock where it passes through the grommet. Use about 5-8CM of tape to start with, wrapped on in a cone moving towards the top of the trap so that it gets thicker. Then when the trap is re-inserted into the grommet, it will expand the rubber more and make a better seal.
Note: This has only been a problem with cheap kit that uses rubber grommets and press on lids. Better fermenting bins have screw tops and large rubber bungs to place the airtrap in.