EDIT: The primer-pumps I mention are manual, hand-operated, with a plunger that works straight up-and-down, just like that found on almost all larger diesel-equipped engines.

I already have such incorporated on the mechanical lift-pump on the engine itself; but, that is way up there on the engine and a long way from the individual tank filters.

Well...., it appears I can't make the hyperlink thingie work; here is the web address of the pumps I speak of:

https://www.amazon.com/gp/product/B0CPP5R1JQ/ref=ask_ql_qh_dp_hza

Any adapter fitting I have found with M16x1.5 Female to either 1/2 or 3/8 NPT Male is beginning at $20 and from there to way up there for a single simple adapter fitting.

I am having no luck finding any similar pumps with normal thread size.

I guess the solution will be try one pump and epoxy it into a TEE.

I am curious as to what type primer-pump you are using; maybe I will like it better than the style I have been considering.

They are manual pumps, right ?

Can you post a link ?

Thanks.

If you prefill your filters before installing them onto the engine you will not usually have any problems you are trying to address. I've been around heavy equipment and trucks for over 50 years and a single priming, lift, transfer pump, (same thing, called differently) with a 10 micron filtered input, followed by a two micron output, (which is input to injection pump) is really all that is needed. 

Much easier to "push" a fluid medium that to "pull" the same. You could install an electric flow through plunger, or diaphragm pump near the fuel source and a prefilter powered with a push button in the operator station and a bleed valve just before the injection pump. You could crack the bleed valve open, operate the priming pump till fuel spills from the bleeder. Once the fuel is flowing from the bleeder port, the filters are full.

Multiple primers in a system is a disaster as when failure occurs there are multiple possibilities suspect. KISS is a very good rule to follow at times.

IMO of course.

I think I found what you describe, sold under a thowwwzand different names and all in the same box with the same photos and descriptions; priced from $8.00 to as much as $30.00.

I like the part about "last forever. I have good luck with them "

You have changed my mind and plan of action --- Thank You.

Plus, I can do three or more filters for what I was fixing to spend on one.

As best I can determine, those are "Flow Through" pumps that do not interfere with what other pumps are doing and can just go along for the ride with fuel passing through them until they are called into action.

When I was planning all this out in my skull, I considered some sort of electric pump; but, my first thoughts were about having to run wires and switches and such for each one and it only ever used when servicing the individual filters --- hence my preference for something manual.

But, now, I have a viable plan where your little electric pumps will work and zero wiring needed --- don't get me wrong, I love wiring and am quite an expert at it; it just isn't going to be necessary for my application.

Everything around here, including the tractors and riding mowers, has several 2-prong pigtails hanging here and there just for such occasions.

I have several 2-wire extension cords equipped with such pigtails at each end; in fact, that is what they were before I converted them = extension cords.

A few of these cords have a weather-proof box with a toggle-switch near one end.

My plan is to leave such a pigtail hanging from each pump; and, I can power the pump by one of my toggle-switched cords.

I was a little hesitant on account of the 5/16 in/out; but, just about any 3/8 fitting (or larger) has an actual inner orifice of closer to 1/4-inch or less.

Thanks for confirming that bit .