[KelseyH]

I would just run a few empty sanitize or washer cleaning cycles (if you have that option) until there are no more suds.

I did that before I prepped our diapers - just out of curiosity - and even though we use HE detergent religiously, after 18 months of daily use there was some detergent buildup and a few suds during the cycle. I'd imagine it would be worse with non HE detergent in the inner workings of the washer. Good luck!