Bill,

Many of the dual-action pumps are labelled In/Out on the ports on the bottom half. However, I have had units that are unlabelled and I have had to use trial-and-error to set them up (there are only two possibilities, so this is not a big problem).

Here are a couple of links that might help:

https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=71137#Post71137

https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=196813#Post196813

Tim