We use Dawn for dishwashing and don't have excess suds when dumping. We still use the plastic dishpans from our tenting days and they just fit in the sink. One for wash, one for rinse. We add a few drops of Dawn while running about 2 inches of hot water into the dishpan and get enough suds for dishwashing. By the time I am done washing dishes the suds are almost gone. I have a short clear piece on the dump connection and I never see excess suds.
As others said, use less Dawn and you should be ok.