I found this article in the intenet..
Installing a Catch Tank
Although an oil catch tank is mandatory for any kind of track work (including ordinary track days), it is a good idea to have one for general road use too. Although you can purchase both aluminium and plastic tank kits for this purpose, it is very easy to make your own at minimal cost.
I used an empty 1 litre plastic oil container and made a hole in the top near the spout to insert a 'breather' pipe as it is vital that the tank does not pressurize. I made the breather pipe an interference fit in the hole and sealed it both inside and out with a generous bead of silicone sealant.
On most engines, you will find a crank case breather and a cam cover breather and these can both be fed to the same catch tank by piping them to the top limbs of a 'Y' joiner and then feeding the bottom of the 'Y' to the catch tank. It is vital that the two breathers remain free to breath to the atmosphere albeit via the breather pipe in the catch tank.
The breather pipe and 'Y' joiner can be obtained from most caravan accessory shops at a very reasonable cost. The container can then be attached to the chassis with large cable ties.