The following are my tips on the easiest way to make sloe gin in large quantities. Firstly only make it in years when the sloes are plentiful but make a lot when you do! There is no point taking ages to pick your sloes, in good years the bushes are festooned with berries and you can rapidly gather them. You should be able to pick enough sloes to make 8 litres of sloe gin in an hour.
On returning with the sloes put them in a sink to wash them and pick off any stems that are left in the berries to prevent the sloe gin getting a woody taste and simply freeze them. This encourages the skins to split thereby avoiding having to prick the sloes with a pin. I then assemble everything needed to make the sloe gin. I use 2 and 3 litre jars that mustards and mayonnaises come in, but I have also bought large half gallon screw top jars from Ebay. I use Constance Spry's ancient recipe so the only other ingredients needed are sugar, gin and ground almonds or (almond essence). Perhaps almond essence is safer to use as it is less likely to give an nut allergy. I buy the cheapest London gin I can find and this year 2009 I paid £10.19 per litre.
I then simply assemble by adding 365 grammes of sugar to a 2 litre jar. Then put on top one and three quarter pints of sloe berries still frozen and add 7 drops of almond essence to which I top up with gin until full. I then put the lid on and give the bottle a good shake to entirely soak the sugar and settle everything down and then top up again until the bottle is brimful. I then store the gin down the cellar shaking the jars occasionally when I remember.
I generally leave the gin for the best part of a year before removing the stones. I have heard that leaving the berries in for along time can cause the gin to taste bitter and woody but have not personally found this and plenty of mine gets left 2 years with no ill effects. On decanting I pour into a sieve over a large jug and allow all the liquid to drain through and throw the berries away. I then simply filtrate the gin to leave it clear by passing it through a cotton hankerchief. Lastly I store the sloe gin in litre water bottles to release the large jars for the next crop of sloes.