Anyone have any good tips/tricks for checking the alignment of a derailleur hanger without the requisite Park/etc tool?

Screwing the longest bolt you can find into it often highlights how squint it is.

Make a tool. Length of angle iron,a bolt, stack of washers or a spacer. and a ruler. One of the cheapest and easiest bike tools to make.

Look at it closesly then reattach singlespeed wheel.

Got a spare rear wheel with a threaded axle?

If so (or can borrow one), remove rear mech and thread spare wheel into hanger – it’s the same thread as your mech.

Spare wheel should be parallel to your wheel – if not, manipulate hanger via spare wheel until they’re parallel.

I think the lifeline tool is about £20.

Depends on the hanger but many have a flat side – take it off and lay it on something flat . If there’s gaps its bent, if it sits flush it is straight. Of course that only works if it can lie flat!

Fit a mech and eyeball it. It’s meant to hang downwards.

If you make a tool the thread is M10x1, which is finer than the M10 that tends to be sold in hardware shops

Depends on the hanger but many have a flat side – take it off and lay it on something flat . If there’s gaps its bent, if it sits flush it is straight. Of course that only works if it can lie flat!

Only works if the dropout is perfectly flat too. Many/most aren’t.

Wheel is the best “bodge”.
Buying the proper tool is quick, cheap and easy.
It’s one of the checks i do when the bikes get a proper service.