Between the 2nd stage and 3rd stage, there should be one drain on that separator and then one on your next filter, which is being fed from the 3rd stage output. If you have a P21/P0, then it has an inbuilt separator - it is essentially a filter housing with a separator inbuilt and two manual drains. If you don't have one of those and the only thing you have is the 31-inch tower, then it may have an inbuilt separator and it may not - depending on the model. You should be able to see it easily enough by taking the top off and removing the filter cartridge - you are most likely looking for a tube with some small holes in it or a bronze filter looking thing, which does the same job. If you don't have an inbuilt separator on the 31-inch tower and you also don't have a P21/P0, then you will need to add a separator or your 31-inch tower dessicant will be destroyed very quickly. It may help if you post a picture of your system. The stock setup has the drain on the final filter P21/P0. I would highly recommend contacting Mike Casey from Lawrence Factor - what Mike doesn't know about filtration probably isn't worth knowing.
It is important that I point out that if your current 31-inch tower doesn't have an inbuilt separator, that you add a separator before your final filter or you will destroy your cartridge dessicant in a very short time, which will then render your activated carbon useless as it will be covered in oil mist, and any hopcalite in your filter for Carbon Monoxide removal will also be rendered useless as it will not function if it is wet, which it will be very quickly by not having a final separator before the final filter.
So to clarify, dessicant is used for moisture removal and is normally 13x molecular sieve, Activated Carbon will take out a host of nasties but will not work with oil on its surface and Hopcalite is used for Carbon Monoxide removal but only works when dry. Hopcalite should always be used if you use a Petrol/Gasoline compressor and is optional but highly desirable if you use an electric drive motor.
Don't mean to scare you but I see some really foolish things being done out there to retrofitted compressors where the person has either cut corners or not understood what is required to ensure that their system continues to deliver breathing grade air over the mid to long term. You should also look for a pressure maintaining valve after your 31-inch tower, which will keep pressure of about 150 bar in your tower after you shut it down. Failure to have this will reduce the lifespan of the dessicant to around a week or so as it will try to dry all the air out in the immediate vicinity. An easy way to check if you have a PMV or not is to purge all of your filters and then start your compressor and time how long it takes to get air out of the whip. It should be around 4 minutes for your setup. If you get air out within a minute, then you have no PMV and should fit one - Mike Casey can help you with this too or any other Lawrence Factor Dealer.
