Approx. 1kg sloes. I have used around 1kg of sloes and a handful of redcurrants.
1 Kg Sugar
2ltrs Gin
1 Demijohn
Pour the sugar into a clean, dry demijohn. Pick over your fruit to make sure you don't have any rotten or dirty fruit. Prick or split the fruit to release their colour and flavour and place in the demijohn. Pour in your gin over the fruit and sugar. Seal the top of the demijohn and give it a good shake making sure to stir everything up. Place the demijohn in a cool dark place for the next three or four months, remembering to give it a good shake every two weeks or so. After three or four months you will find that all the sugar has dissolved and the berries have all sunk to the bottom.
Here is my sloe gin just before it was given a nice shake.

Here is some sloe gin that I made a few years ago that was nearing maturity ready for bottling. As you can see it soon gets a lovely colour.

You will find that when you have syphoned off your sloe gin you are left with about 25mm - 50mm of berries and sediment which also contains an amount of gin. To use this small amount up, simply fill the demijohn back up (leaving an air gap) with rough cider (proper cider not Strongbow or the like). You will need to add an air lock because you may reactivate any yeast which is present in the cider and you don't want any explosions! After about three weeks this "slider" will either stop bubbling or will have absorbed enough flavourings and colour to be ready to drink. If it hasn't stopped bubbling you can either wait until it's finished or pop a camden tablet into the liquid to kill the yeast.
Here's my sloe gin at about three weeks old.

As you can see, it already has a nice claret type colour to it.
I decided to bottle up my sloe gin and make some slider using my own cider. I had to make up an impromptu bottling plant so I emptied out one of the wall units to put the sloe gin in which then made syphoning that much easier.

I managed to get hold of some decent looking bottles for my sloe gin.

Look at the colour! I think the inclusion of a hand full of red currants has added to the finished article.

Here's the first few bottles already filled.

After eventually syphoning all the usable sloe gin away I was left with just the berries and about a pint or so of sloe gin. This was now time to make the slider. Here is just under a gallon of our own cider. This cider is about three months away from being totally ready but is quite quaffable right now.

Here is the slider after a good shake. Having never made this stuff before I would presume this will be ready in about three weeks. I will be putting an air lock into the demijohn because there is live yeast in the cider and I don't want any explosions. I may have to drop a camden tablet into the brew to kill off the yeast because I don't want this drink too dry. I would also imagine that it would be fairly high in alcohol - I just hope the natural yeasts can cope with this.

Here is my afternoon endeavours.

Good times will be had!!