Covering the Vessels
This is an elementary precaution almost anyone would take. But it is surprising how many would overlook the necessity. The mash tun (polythene pail), should be covered with a sheet of strong polythene with no holes in it. This should be tied down with strong string or, better still, a strong elastic band or several linked together and joined by a small wire clip or hook. This will hold the covering in place tightly so that air and airborne diseases cannot gain access.
The fermenting vessel must be covered in a similar fashion. The covering on this will billow up like a balloon under pressure from the gas generated. The gas will find an outlet for itself, keeping up a constant out-going stream to prevent diseases entering.