How to reduce pure ammonia

My suggestion is don't. Do not use ammonia as a thinner. Distilled water is far safer and available worldwide. Ammonia has lethal consequences.

Another substance is automotive windshield washer fluid. Just use in a well ventilated area. Fill a squeeze bottle (I use the ones my wife throws away that here contact lens solution comes in) for easy dispersal and storage. 

I don't think he is intending to use ammonia as a thinner, only as a cleaning aid.

Laundry ammonia is available (at least in Canada) and can be thinned with nothing more than plain water. If it's safe enough for housewives...

Windex with ammonia is basically 85% water, 12% Isopropyl Alcohol and 3% Ammonia with a few drops of blue color added.

I suspect that the cleaning is enhanced by ammonia, but also requires the Isopropyl Alcohol. 

Whatever you decide DON'T MIX WITH CHLORINE BLEACH! Very nasty things can happen depending on the ratio, from burning your lungs to an explosion.