This method won't work on 04-up models as they have no timing hole plug.
Basically you need some clear vinyl hose and a nipple fitting to replace the timing hole plug.

A 3/8“ flare to 1/4” FPT fitting with a 1/4“ MPT to 3/8” hose barb (left pic below) can be used in place of the timing plug.
The 3/8“x18 pipe fitting's threads apparently work out to fit in the 5/8”x18 threaded hole.

In the center and right pics below basically show a modded 3/8“ hose bib with an 1/8” hose bib fitting screwed into it.
The hose bib was cut off, the ID drilled 11/32“ and the hole threaded with a 1/8”x27 tapered pipe thread tap for the smaller fitting.
You can buy a 3/8“ to 1/8” bushing to accomplish the same thing.

In this case, the taper bushing was ran it into a 5/8×18“ die for a straight cut to use with a washer but the tapered fitting will do. ¹⁾
The hole in a 5/16” stainless washer was enlarged to 5/8“ to go up on the bushing.
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The slack tube below is made from 1/8” clear Tygon vinyl tubing and a 2×4 app 3 feet long. ⁵⁾
The backing plate is a 2×4 with an aluminum 36“ ruler attached with drywall screws.
The two rulers below (right pic below) show the measurements on the wooden ruler to be 1/8“ longer than the steel one in a 36” run.
Ambient temps can also shrink or expand the ruler whether wooden or aluminum so that has to be taken into account of subsequent tests.

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The drywall screws were also used to bind the hose between the ruler and the shank using the screw head to hold the hose down. ⁸⁾
The black connector at the top is a cut down spark plug boot used as a sleeve for the hose connections.
(technically if you buy enough length of hose, you don't need the connector)
Just make sure all connections are sealed good.
The engine will suck on the hose for the most part in varying degrees so there's not enough pressure to blow off the hose.
A small piece of plywood screwed to the bottom of the 2×4 makes a nice stand for the unit.
Then all you have to do is remove the timing plug, install the new fitting and hook the hose end to it.

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