We do not currently clean the pump
between our moms unless something has spilled on it.

I know nothing about the particular pump, and very little about this issue,
but in a review done for Wellstart a few years ago I found literature
making it clear that aerosols of breastmilk travel a long way and that
contamination has been documented well away from areas that contact the
breast or that are obviously likely to get dirty: I assume that it's
because these can provide a locus for bugs to breed and spread via air that
there can be a problem...
A microbiological audit might be a good idea.

Maureen Minchin, IBCLC. Christ Church Vicarage, 14 Acland St., St.Kilda,
Vic. 3182 Australia. tel/fax: 61 3 9537 2640
"Taking paths of least resistance is what makes rivers - and people -
crooked." poster in Palmerston North NZ bookshop...