We have a Seho wave soldering machine and cannot seem to get rid of dross that is being generated within the solder pot, and is being pumped out in the wave. It is not the same kind of dross that forms on the surface of the solder pot(this is very much under control.) The stuff being pumped up is brownish in colour and seems to develop on the stainless steel surfaces in the pot. Is this an oxide from the stainless steel, or perhaps a bad batch of solder? I have drained the machine and cleaned out all the pumps etc, and am wondering if I should use new solder now. I am planning to use the Alpha vacculoy bars.

Any comments/help will be appreciated.

Many thanks in advance.