The procedure in which tubes can be "flushed" is a HSG (a type of x-ray), not a hysteroscopy. A hysteroscopy just involves a camera being inserted, whereas with the HSG your uterus is filled with dye (and the dye is observed passing through the tubes). Could it be the HSG you are meaning?

I'm guessing the surgery is probably a laparoscopy. That is used to diagnose endo and also identify a number of physical impediments to pregnancy. I had one in 2010. We changed to a new FS after 4 failed IVF (plus 1 FET) and when our new FS did the lap I was diagnosed with stage III endo (which I had long suspected, but our first FS refused to do the lap to investigate it). We did our 5th IVF 2 months later and that gave us DD. I'm convinced the lap is the reason that IVF worked. I also had a hysteroscopy done at the same time. I'm actually booked to have another laparoscopy and hysteroscopy in early August because my endo symptoms have returned.

If your Dr is recommending a lap, I have a page of suggestions on my blog for making the recovery a little easier. I'm also happy to answer any questions about my experience last time.

Have you had any testing done for clotting or immune issues? That's another area to investigate, although some Drs don't "believe" in it.