I used the 1.5" to 1" adapter, and because Dometic says not to put the adapter close to the pump it had to go close to the thru-hull... I put in all new hose between the new pump and the thru-hull, because the old run was 1". So I also decided to replace the remaining short length of 10-year-old white 1" hose with about 6" of new Trident hose (heavy-duty wire and cloth reinforced, black with green stripe). That old white hose was impossible to pull off the thru-hull (until I softened it with a small butane flame and cut the ribs with a razor). The new stuff went in easy and all was double-clamped.

I had pulled the old pump put yesterday when it was a bit warmer and sunnier (a nasty job)... think it's time to postpone any further projects for mid-40's weather and above.