Exactly what it sounds like.
I ended up using the Dickinson one which was pricey but small and looks smart, and also has a shutoff switch on it.
Here it is installed.
I had to interrupt the copper tubing and flare it to connect – here is the flaring kit in full swing
And here it is fully installed
Not hard to do, just messy. I burned all the fuel from the tank using the heater, but some still dribbled out. In addition, I didn’t put one of the flare fittings on correctly, so when I ran the pump, diesel squirted everywhere, arrghgh.
Luckily, if you are going to squirt highly explosive fuel everywhere, diesel is not a bad one to do it with, being a lot harder to light or make explode than petrol (gasoline) or propane.