We always use stainless steel bushings 304 (1/2"M x 3/8" F) when going from 1/2" to 3/8. Steel bushing are thin because of the dual thread pattern (inside and out) and tend to rust quickly when used in water service.
Andy W
John,
If your surface washer has a height adjustment raise the spray bar height. I did this years ago and it helped on one of my units that did the same thing. Also, I agree with most of the other comments so try them too.
Hope this helps,
Andy
You can usually get efflorescence from brick by using a hyrochloric/muratic based cleaner. It is caused by moisture behind the brick pushing salts to the surface. Wet brick lightly, spray 10 to 20% solution and rinse. It may take several applications to remove. Do a test spot first as this can be a tricky business depending on your brick/mortar combinations. Hope this helps.
Andy