What to do...

[CJH]

Having read this a few times now, I'm missing something fundamental (haven't touched the claret tonight so I can't blame the vino), hoping someone will point out the obvious (not to me). How will flushing out the system with a hose solve the problem of leaking head seals? The suspense is killing me.

Tsk. You're quoting me (incorrectly I might add) out of context. It'll make more sense if you read it in the context of the bit of Smosh's post that I was responding to.

The van is losing water.....

If the rubber seals between the heads and the case are dry, then this is a simple if painstaking fix.

Actually I missed a bit that's perhaps important.

After a few short runs the water is brown, and foamy.

Foamy isn't good. Possible leaking cylinder seals? Or could it just be air getting in at a leaking hose union, say near the water pump - would that make it foamy?

[what2do]

Ahh, a moment of clarity at last. Despite rereading it several times I still misinterpreted your point. All's well that ends well.

[Smosh]

Well the weather is miserable but I did the compression test. Didn't fancy getting under the van today tho as I probably would have needed a snorkel!
Front left: 160psi 11 bar
Read left: 180psi 12.2 bar
Rear right: 175psi 12 bar
Front right: 150psi 10.5bar

Not sure what any of that means!

[itchyfeet]

Well it doesn't guarantee a head seal hasn't failed but it looks ok.
need to look for ths leak(s) next.
If you fill with water and bleed the system, run it until the rad fan kicks in, if if all boils over thats bad, if it doesn't thats good.
let it cool, fill up again to brim and repeat.