Bosch WFVC VISION 16 Repair Instructions page 18

4.2.16 Drain non-return assembly and sump
The drain non-return assembly prevents waste water from entering
washers. It doesn't use a reservoir to provide better suds removal.
The drain non-return assembly and sump were designed to provide
superior suds removal due to the number of cases of excessive
detergent usage.
Oversudsing occurs from excessive detergent usage or using the
wrong type of detergent. When encountering oversudsing, advise
customers to use less detergent and use a detergent for front loading
washers (with "HE" on the package).
4.2.16.1 Drain non-return assembly
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4.2.16.2 Sump
The sump has a large opening and doesn't have a sump ball to
remove suds more efficiently.
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