1.  Materials used for permeable grog are clay and a fine grained combustible, 300 mesh or greater.  In the Nepal Purifier Project the combustible in use is wheat flour because this is commonly available.  The ratio of dry material in use is 63 clay to 37 flour.  Water content is 20% (indicated as a percentage of the 100% dry material composition).  In this case we think of the composition as 63 parts clay, 37 parts flour and 20 parts water.
2.  Mix well the 63 parts of clay with the 20 parts of water, then seal this in a plastic bag over night.  So, for example, for every 630 grs. of clay use 200 mls. of water.  Soaking over night is an aid to good plasticity.  Note that it is not possible to follow a more conventional approach to mixing, combining clay, flour and water at the same time.  The reason for this is that clay particles flock together taking in most of the water, while little water goes to the clay.  Note that depending on location, and for future work it may be a good idea to do local assessment of the possibility of a combustible other than one that is gluttonous.  This may save considerable work in the grog material processing.
3.  The following day intensively mix the flour in with the wet clay.  Using the same example, the 630 grs. of clay and 200 mls. of water has given 830 grams of wet clay.  To this add 370 grs of flour.  In the initial, experimental period this mixing would best be done by hand, simple machines not yet indicated, though this involves a lot of work.  As the flour adheres to small lumps of clay the whole appears as a kind of white.  Each and every such lump needs to be broken thoroughly by hand, a last step in mixing is to push all the material through a ten mesh screen.  The material is then ready for pressing. 
4. Press the grog composition into disks or tiles of a couple of centimeters thickness, then dry these for several days.
5.  Fire the disks in a kiln upto the 'maturing temperature' of the clay, that is to say to the point of optimal strength.  Since there is a lot of smoke in this process the firing should be done outdoors, preferrably in a rural area.  For common pottery clays the maturing temperature may be between about 900 centigrade and 1050, depending on the clay.  It is important to understand that the critical temperature range for slow firing is around the ignition point of the combustible.  So for flour, at about 500C when the first smoke appears, it is necessary to hold this temperature until somewhat after all smoke is gone (perhaps 60 minutes).  To go through this range too quickly results in the disks breaking, indicated by a pile of particles when the kiln is opened.  This is not a good idea, since the inside of the pile would not have reached the desired temperature.
6. It will now be a simple matter to break the disks up, the more so because they are very porous.  But smaller bits are not so easily crushed by hand.  It is best to use a mill for this, with a caution:  do not breath the grog dust.  Rather, use a good quality respirator.  After the milling the resultant powder should be 30 mesh and should have good particle size distribution, some right at 30 mesh and some a lot finer.  The grog powder is now ready for use in the purifier composition.

1.  The percentage composition of clay and grog materials will vary from one clay to another, so small, trial batches must first be run.  But a typical composition may include 50% each of the clay and the grog.  Mix the dry materials well.
2.  Water content can also be varied a little, but 10% can be quite appropriate.  The best way to add this is a little at a time, with intensive hand mixing of all the material during the intervals between additions of water.  By contrast, adding a lot of the water at once would make some particles too wet and others too dry, so this should be avoided.
3.  Pressing can now be undertaken, the material ready.  As with the disks one may want to take several days to dry the purifiers.  But at some future point one may decide to skip the drying.  The permeable body tends to be so open that it gives up it's water very quickly in the early stages of firing.
4.  Fire to optimal strength, the maturing temperature of the particular clay.  Following firing the purifiers are ready for saturation with colloidal silver.  Following drying the purifiers are ready for testing.  With fine tuning of variables the purifiers should be ready for use following saturation, then following drying.